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The metabolism of histidine. Liver-enzyme changes during development
282
BIOCHIMICA ET BIOPHYSICAACTA BBA 25065
T H E M E T A B O L I S M OF H I S T I D I N E . LIVER-ENZYME CHANGES DURING DEVELOPMENT RHODA MAKOFF* AND ROBERT C. BALDRIDGE Department of Biochemistry, Temple University School of Medicine, Philadelphia1, Pa. (U.S.A.) (Received December Ioth, i963)
SUMMARY In contrast to L-histidine ammonia-lyase (EC 4.3.I.3) activity which is barely detectable at birth and remains low for the first 2-3 weeks of life, L-histidine-pyruvate transaminase is readily detectable in the liver of the rat fetus on the I7th day of gestation and increases during the ensuing 4 days so that by 12 h prior to parturition the activity is one-third that found in weanling rats. By 24 h after birth, the levels are almost the same as those found in the livers of adult rats. Levels of both liver histidine-pyruvate transaminase and histidine ammonialyase are higher in adult female than in male rats; they are also higher in pregnant rats than in non-pregnant females of the same age.
INTRODUCTION Histidine, in addition to being converted to compounds such as histamine and carnosine, is degraded by straight deamination 1 and by transamination 2. Under normal circumstances in adult animals, a large proportion of histidine is considered to be deaminated by L-histidine ammonia-lyase (EC 4.3.I.3, also known as histidase) to form urocanatO which is then converted to forminoglutamate and ultimately to glutamate. In humans with histidinemia, who lack histidine ammonia-lyase 3,4 the major route of catabolism is apparently via transamination, with the accumulation of imidazole pyruvate, imidazole lactate and imidazole acetate. As AUERBACHAND WAISMAN5 had observed that liver histidine ammonia-lyase activity of the rat is quite low at birth and for 3 weeks thereafter, we decided to inquire into the levels of L-histidine-pyruvate transaminase in the liver during various periods of development. It was found that a considerable potential for transamination is present during the fetal and neonatal periods when there is a relative lack of the enzyme which catalyzes the straight deamination of histidine. As a part of other studies of variations in levels of histidine-catabolizing enzymes, measurements were made to determine whether the sex difference noted 5 for liver histidine ammonia-lyase levels (females > males) also applied to levels of histidinepyruvate transaminase; such a difference was found to occur and is magnified during pregnancy. * Present address: Department of Biological Chemistry, Harvard Medical School, Cambridge, Mass. (U.S.A.). Biochim. Biophys. Acla, 90 (I964) 282-286
283
ItlSTIDINE METABOLISM EXPERIMENTAL PROCEDURE
Pregnant rats of the Wistar strain were obtained from Huntingdon Farms; the gestation day was calculated from the time of mating. Newborn pups were nursed for 21 days and then put in separate cages and fed Purina chow. All other rats were fed the chow except for nursing mothers who were fed a laboratory diet which contained 20 % casein. Although liver tissue could be detected at the I5th day of gestation, the amount was not considered adequate for analysis, hence complete fetuses were analyzed at this time. From the I7th gestational day up to 18 days following parturition, the livers of litter mates were pooled for analysis; at least 2 litters were used at each age studied. In older rats, individual livers were analyzed. Levels of histidine ammonialyase, urocanase (urocanate (imidazolonepropionate) hydro-lyase) and histidinepyruvate transaminase were measured as described previouslys with the incubation mixtures maintained at 3°0 . RESULTS
Prenatal enzyme development The results of measurements of hi~tidine ammonia-lyase, urocanase and histidinepyruvate transaminase in the fetuses are shown in Fig. I. On the I4th or ISth day of gestation no activities were detected. On the I7th and I9th day histidine ammonialyase and urocanase were barely discernible, whereas there was considerable trans-
150
/ / / /
"~ 1 0 0 /
/ |
~
././
,, 12
/
Oir~:h
..... ! 14 16 18 Gestotion (doys)
20
22
Fig. i. E n z y m e c h a n g e s d u r i n g p r e n a t a l d e v e l o p m e n t of t h e rat. T h e o r d i n a t e refers to m f f m o l e s of s u b s t r a t e d e s t r o y e d or of p r o d u c t f o r m e d p e r m i n per g of f e t u s on t h e i 5 t h g e s t a t i o n a l d a y or of liver a f t e r t h e I s t h g e s t a t i o n a l day. M e a s u r e m e n t s were m a d e as described p r e v i o u s l y s. T h e f e t u s e s f r o m 3 litters were pooled for analysis. L i v e r s f r o m i n d i v i d u a l litters were pooled for s u b s e q u e n t a n a l y s e s . 3, 2 a n d 6 litters were u s e d on t h e ITth, I g t h a n d l a s t d a y s of g e s t a t i o n r e s p e c t i v e l y ; a v e r a g e v a l u e s are s h o w n . • - - - • , histidine ammonia-lyase; m--m, urocanase; a n d ~ k ' - - " ~k, h i s t i d i n e - p y r u v a t e t r a n s a m i n a s e .
aminase activity. By the 2Ist or 22nd day (within 12 h of expected parturition) histidine-pyruvate transaminase levels had increased to one-third or more of the levels found in weanling rats. Urocanase activity was increased somewhat immediately prior to birth but histidine ammonia-lyase was not.
Enzyme development in the weanling rat In Fig. 2 are shown the levels of the three enzymes in the livers of animals from birth to I month of age. 24 h following parturition, histidine-pyruvate transaminase Biochim. Biophys. Acta, 90 (1964) 282-286
284
R. MAKOFF, R. C. BALDRIDGE
levels rose to values near those found in adult animals. Urocanase activity was considerably higher than that of histidine ammonia-lyase at time of parturition and increased slowly throughout the Ist month of life. As previously reported 5 the histidine ammonia-lyase content of the livers was negligible at birth and remained low for the following 2-3 weeks. 8O0 f Parturition
700 ~' 6 0 0
>
•
/t
~- 5oo E -400 300
E~200 •
100
•
•
•
•
IIII
•
5
9
13 17 Days
2'1
A
' 3O
Fig. 2. P o s t n a t a l e n z y m e d e v e l o p m e n t in the first m o n t h . The ordinate refers to m/~moles of s u b s t r a t e destroyed or of p r o d u c t formed per min per g of liver 6. Livers from littermates were pooled for analysis w i t h r a t s up to ~8 days old ; the average of values obtained from a t least 2 litters is s h o w n for each age. S u b s e q u e n t analyses were made w i t h livers from individual animals; the average of values for 4 or more animals of each age is shown. Histidine a m m o n i a - l y a s e ( • = 9, O = c~); urocanase ( B ) a n d h i s t i d i n e - p y r u v a t e t r a n s a m i n a s e (~k = £, & = ~).
Enzyme development in the adult rat Fig. 3 illustrates the relative activities of the enzymes in the livers of non-pregnant females up to 250 days and of males up to 395 days of age. At 200 days, the activity of h i s t i d i n e - p y r u v a t e transaminase, like that of histidine ammonia-lyase was signifi-
L 1000 .~ 900
"~ .E 7oo E
&
&
•
•
&
&
&
_~500 t
30(] o
100
o
¢ I
100
1;0
200
250
I
300
3;0
Days
Fig. 3. Comparison of e n z y m e activities in a d u l t male and female rats. The ordinate refers to re#moles of s u b s t r a t e destroyed or of p r o d u c t formed per rain per g of liver ~. The values represent averages o b t a i n e d w i t h 4 or more animals of each sex a t the ages shown. The difference b e t w e e n the levels in males a n d females was significant (P < o.o~) in t h e case of b o t h histidine a m m o n i a lyase a n d h i s t i d i n e - p y r u v a t e t r a n s a m i n a s e f r o m 5 ° to 200 days of age. Urocanase levels were similar in males a n d females, hence only one value is shown. D a t a were n o t o b t a i n e d w i t h females older t h a n 200 days. Histidine a m m o n i a - l y a s e ( • = ~, O = C7) ; urocanase ( • ) a n d h i s t i d i n e p y r u v a t e t r a n s a m i n a s e (A = £, & = ~).
Biochim. Biophys. Acta, 90 (1964) 282-286
HISTIDINE METABOLISM
285
cantly higher in females than in males. Urocanase levels, which remained fairly constant from birth up to 50 days of age, increased somewhat between the I l o t h and 2ooth day. There was no significant difference between the activities of urocanase in males and in females.
Enzyme activities during pregnancy The activities of both histidine ammonia-lyase and of histidine-pyruvate transaminase were significantly higher in the livers of pregnant females immediately prior to parturition than in those of non-pregnant females of the same age (Table I). Neither histidine ammonia-lyase, urocanase, nor histidine-pyruvate transaminase could be detected in rat placenta. That no inhibitors were present in the placental extracts was shown b y addition of the latter to incubation mixtures containing liver homogenates with no diminution of activity. TABLE
I
HISTIDINE AMMONIA-LYASE AND HISTIDINE--PYRUVATE TRANSAMINASE LEVELS IN LIVERS OF PREGNANT RATS R a t s were k i l l e d on t h e 21 s t or 2 2rid g e s t a t i o n a l d a y (I 2 h p r i o r t o e x p e c t e d p a r t u r i t i o n ) . L i v e r s f r o m 5 p r e g n a n t a n d f r o m 6 n o n p r e g n a n t f e m a l e s were a n a l y z e d . U n i t s of e n z y m e a c t i v i t y are de fi ne d as m / , m o l e s of p r o d u c t f o r m e d p e r rain p e r g of l i v e r s. T h e a v e r a g e w e i g h t s of l i v e r w e re 4-5 a n d 4.1 g p e r i o o g of b o d y w e i g h t for t h e a n i m a l s i n e a c h group. V a l u e s i n c l u d e t h e s t a n d a r d error of t h e mea n.
Age (days)
Pregnant Non-pregnant females
Body weight (g)
Histidi~t,e Histidineammonia-lyase pymvate tran*ami~ase (units per g liver) (units per g liver)
9o-12o
297 4- 8
646 4- 66
9oo -4- 5 o .
IOO-iio
243 4- 6
388 4- 46
666 4- 43
DISCUSSION
The control mechanisms involved in the initiation of the synthesis of specific enzyme proteins in the fetus and newborn remain essentially unknown. I t seems reasonable to assume that more than one factor is involved as there is considerable variation in the times of appearance of various enzymes. The activity of several transaminases in addition to histidine-pyruvate increases at or near parturition; these include t y r o s i n e ~-ketoglutarate transaminase (EC 2.6.1.5) 7 and p h e n y l a l a n i n e - p y r u v a t e and phenylalanine-~-ketoglutarate transaminases 5. A second group of amino acid-catabolizing enzymes appears later; phenylalanine hydroxylase (EC 1.99.1.2 ) becomes measurably active between the 4th and I2th day following parturition 8 and t r y p t o p h a n pyrrolase (EC 1.11.1.4) apparently does not develop to any extent in the rat until some 15 days following birth 9. As histidine ammonia-lyase is barely detectable at birth it would seem to fall in the latter category. It is of interest that enzymes which catalyze consecutive steps of a single p a t h w a y do not necessarily develop at the same time, as observed in the present case in which the development of histidine ammonia-lyase was observed to lag behind that of urocanase. I t is not possible on the basis of available information to assess the relative B i o c h i m . B i o p h y s . A c t a , 9o (1964) 2 8 2 - 2 8 6
286
R. MAKOFF, R. C. BALDRIDGE
amounts of histidine which are degraded by the alternate metabolic pathways at early stages of development. However, it is apparent that histidine-pyruvate transaminase reaches peak activity long before histidase does, and, based upon enzyme activities, the potential for transamination is some 20- or 3o-fold greater than that for straight deamination immediately prior to birth and during the neonatal period. As mentioned previously 6, the intracellular concentrations of pyruvate would undoubtedly be a limiting factor in the amounts of histidine which undergo transamination. The fact that the levels of both histidine ammonia-lyase and of histidinepyruvate transaminase are greater in female than in male rats, coupled with the observation that the levels are higher in pregnant than in non-pregnant females, leads to the suspicion that the activity of both enzymes is related to the estrogen: androgen ratio in the tissues. In recent studies of the sex difference (females > males) in levels of the methionine-methyl activating system, NATORI1° found that the difference was abolished by castration of the male rats and could be restored by administration of androgen. Increased activities of several enzymes in rat liver, e.g., tyrosine transaminase 7, have been noted during pregnancy. Information concerning possible similar changes in the levels of histidine-catabolizing enzymes in the human during pregnancy would be of interest in view of the well-known histidinuria of pregnancy. The original findings of EDLBACHER AND HEITZ11 concerning unchanged "histidase" levels during human pregnancy were based on analyses of autopsy tissue by a non-specific method. ACKNOWLEDGEMENT
This work was supported by Grant No. A65o from the National Institutes of Health, U.S. Public Health Service. REFERENCES 1 A. H. MEHLER AND H. TABOR, J. Biol. Chem., 2Ol (1953) 775. E. V. ROWSELL, Biochem. ]., 64 (1956) 246. 3 V. H. AUERBACH, A. M. DIGEoRGE, R. C. BALDRIDGE, C. D. TOURTELOTTE AND M. P. BRIGHAM, J. Pedlar., 6o (1962) 487 . 4 B. N. LADU, R. R. HOWELL, G. A. JACOBY, J. E. SEEGMILLER AND V. G. ZANNONI, Biochem. Biophys. Res. Commun., 7 (1962) 398. 5 V. H. AUERBACH AND H. WAISMAN, J. Biol. Chem., 234 (1959) 3o4 . 6 p. D. SPOLTER AND R. C. BALDRIDGE, J. Biol. Chem., 238 (1963) 2o71. 7 F. SERENI, F. KENNEY AND N. KRETCHMER, f . Biol. Chem., 234 (1959) 6o9. 8 R. T. KENNEY', G. H. REEM AND N. KRETCHMER, Science, 127 (i958) 86. 9 A. NEMETH, J. Biol. Chem., 234 (1959) 2921. 10 y . NATORI, J. Biol. Chem., 238 (1963) 2075. 11 S. EDLBACHER AND V. L. HEITZ, Z. Physiol. Chem., 276 (1942) 117.
Biochim. Biophys. Acta, 90 (1964) 282-286
BIOCHIMICA ET BIOPHYSICAACTA BBA 25065
T H E M E T A B O L I S M OF H I S T I D I N E . LIVER-ENZYME CHANGES DURING DEVELOPMENT RHODA MAKOFF* AND ROBERT C. BALDRIDGE Department of Biochemistry, Temple University School of Medicine, Philadelphia1, Pa. (U.S.A.) (Received December Ioth, i963)
SUMMARY In contrast to L-histidine ammonia-lyase (EC 4.3.I.3) activity which is barely detectable at birth and remains low for the first 2-3 weeks of life, L-histidine-pyruvate transaminase is readily detectable in the liver of the rat fetus on the I7th day of gestation and increases during the ensuing 4 days so that by 12 h prior to parturition the activity is one-third that found in weanling rats. By 24 h after birth, the levels are almost the same as those found in the livers of adult rats. Levels of both liver histidine-pyruvate transaminase and histidine ammonialyase are higher in adult female than in male rats; they are also higher in pregnant rats than in non-pregnant females of the same age.
INTRODUCTION Histidine, in addition to being converted to compounds such as histamine and carnosine, is degraded by straight deamination 1 and by transamination 2. Under normal circumstances in adult animals, a large proportion of histidine is considered to be deaminated by L-histidine ammonia-lyase (EC 4.3.I.3, also known as histidase) to form urocanatO which is then converted to forminoglutamate and ultimately to glutamate. In humans with histidinemia, who lack histidine ammonia-lyase 3,4 the major route of catabolism is apparently via transamination, with the accumulation of imidazole pyruvate, imidazole lactate and imidazole acetate. As AUERBACHAND WAISMAN5 had observed that liver histidine ammonia-lyase activity of the rat is quite low at birth and for 3 weeks thereafter, we decided to inquire into the levels of L-histidine-pyruvate transaminase in the liver during various periods of development. It was found that a considerable potential for transamination is present during the fetal and neonatal periods when there is a relative lack of the enzyme which catalyzes the straight deamination of histidine. As a part of other studies of variations in levels of histidine-catabolizing enzymes, measurements were made to determine whether the sex difference noted 5 for liver histidine ammonia-lyase levels (females > males) also applied to levels of histidinepyruvate transaminase; such a difference was found to occur and is magnified during pregnancy. * Present address: Department of Biological Chemistry, Harvard Medical School, Cambridge, Mass. (U.S.A.). Biochim. Biophys. Acla, 90 (I964) 282-286
283
ItlSTIDINE METABOLISM EXPERIMENTAL PROCEDURE
Pregnant rats of the Wistar strain were obtained from Huntingdon Farms; the gestation day was calculated from the time of mating. Newborn pups were nursed for 21 days and then put in separate cages and fed Purina chow. All other rats were fed the chow except for nursing mothers who were fed a laboratory diet which contained 20 % casein. Although liver tissue could be detected at the I5th day of gestation, the amount was not considered adequate for analysis, hence complete fetuses were analyzed at this time. From the I7th gestational day up to 18 days following parturition, the livers of litter mates were pooled for analysis; at least 2 litters were used at each age studied. In older rats, individual livers were analyzed. Levels of histidine ammonialyase, urocanase (urocanate (imidazolonepropionate) hydro-lyase) and histidinepyruvate transaminase were measured as described previouslys with the incubation mixtures maintained at 3°0 . RESULTS
Prenatal enzyme development The results of measurements of hi~tidine ammonia-lyase, urocanase and histidinepyruvate transaminase in the fetuses are shown in Fig. I. On the I4th or ISth day of gestation no activities were detected. On the I7th and I9th day histidine ammonialyase and urocanase were barely discernible, whereas there was considerable trans-
150
/ / / /
"~ 1 0 0 /
/ |
~
././
,, 12
/
Oir~:h
..... ! 14 16 18 Gestotion (doys)
20
22
Fig. i. E n z y m e c h a n g e s d u r i n g p r e n a t a l d e v e l o p m e n t of t h e rat. T h e o r d i n a t e refers to m f f m o l e s of s u b s t r a t e d e s t r o y e d or of p r o d u c t f o r m e d p e r m i n per g of f e t u s on t h e i 5 t h g e s t a t i o n a l d a y or of liver a f t e r t h e I s t h g e s t a t i o n a l day. M e a s u r e m e n t s were m a d e as described p r e v i o u s l y s. T h e f e t u s e s f r o m 3 litters were pooled for analysis. L i v e r s f r o m i n d i v i d u a l litters were pooled for s u b s e q u e n t a n a l y s e s . 3, 2 a n d 6 litters were u s e d on t h e ITth, I g t h a n d l a s t d a y s of g e s t a t i o n r e s p e c t i v e l y ; a v e r a g e v a l u e s are s h o w n . • - - - • , histidine ammonia-lyase; m--m, urocanase; a n d ~ k ' - - " ~k, h i s t i d i n e - p y r u v a t e t r a n s a m i n a s e .
aminase activity. By the 2Ist or 22nd day (within 12 h of expected parturition) histidine-pyruvate transaminase levels had increased to one-third or more of the levels found in weanling rats. Urocanase activity was increased somewhat immediately prior to birth but histidine ammonia-lyase was not.
Enzyme development in the weanling rat In Fig. 2 are shown the levels of the three enzymes in the livers of animals from birth to I month of age. 24 h following parturition, histidine-pyruvate transaminase Biochim. Biophys. Acta, 90 (1964) 282-286
284
R. MAKOFF, R. C. BALDRIDGE
levels rose to values near those found in adult animals. Urocanase activity was considerably higher than that of histidine ammonia-lyase at time of parturition and increased slowly throughout the Ist month of life. As previously reported 5 the histidine ammonia-lyase content of the livers was negligible at birth and remained low for the following 2-3 weeks. 8O0 f Parturition
700 ~' 6 0 0
>
•
/t
~- 5oo E -400 300
E~200 •
100
•
•
•
•
IIII
•
5
9
13 17 Days
2'1
A
' 3O
Fig. 2. P o s t n a t a l e n z y m e d e v e l o p m e n t in the first m o n t h . The ordinate refers to m/~moles of s u b s t r a t e destroyed or of p r o d u c t formed per min per g of liver 6. Livers from littermates were pooled for analysis w i t h r a t s up to ~8 days old ; the average of values obtained from a t least 2 litters is s h o w n for each age. S u b s e q u e n t analyses were made w i t h livers from individual animals; the average of values for 4 or more animals of each age is shown. Histidine a m m o n i a - l y a s e ( • = 9, O = c~); urocanase ( B ) a n d h i s t i d i n e - p y r u v a t e t r a n s a m i n a s e (~k = £, & = ~).
Enzyme development in the adult rat Fig. 3 illustrates the relative activities of the enzymes in the livers of non-pregnant females up to 250 days and of males up to 395 days of age. At 200 days, the activity of h i s t i d i n e - p y r u v a t e transaminase, like that of histidine ammonia-lyase was signifi-
L 1000 .~ 900
"~ .E 7oo E
&
&
•
•
&
&
&
_~500 t
30(] o
100
o
¢ I
100
1;0
200
250
I
300
3;0
Days
Fig. 3. Comparison of e n z y m e activities in a d u l t male and female rats. The ordinate refers to re#moles of s u b s t r a t e destroyed or of p r o d u c t formed per rain per g of liver ~. The values represent averages o b t a i n e d w i t h 4 or more animals of each sex a t the ages shown. The difference b e t w e e n the levels in males a n d females was significant (P < o.o~) in t h e case of b o t h histidine a m m o n i a lyase a n d h i s t i d i n e - p y r u v a t e t r a n s a m i n a s e f r o m 5 ° to 200 days of age. Urocanase levels were similar in males a n d females, hence only one value is shown. D a t a were n o t o b t a i n e d w i t h females older t h a n 200 days. Histidine a m m o n i a - l y a s e ( • = ~, O = C7) ; urocanase ( • ) a n d h i s t i d i n e p y r u v a t e t r a n s a m i n a s e (A = £, & = ~).
Biochim. Biophys. Acta, 90 (1964) 282-286
HISTIDINE METABOLISM
285
cantly higher in females than in males. Urocanase levels, which remained fairly constant from birth up to 50 days of age, increased somewhat between the I l o t h and 2ooth day. There was no significant difference between the activities of urocanase in males and in females.
Enzyme activities during pregnancy The activities of both histidine ammonia-lyase and of histidine-pyruvate transaminase were significantly higher in the livers of pregnant females immediately prior to parturition than in those of non-pregnant females of the same age (Table I). Neither histidine ammonia-lyase, urocanase, nor histidine-pyruvate transaminase could be detected in rat placenta. That no inhibitors were present in the placental extracts was shown b y addition of the latter to incubation mixtures containing liver homogenates with no diminution of activity. TABLE
I
HISTIDINE AMMONIA-LYASE AND HISTIDINE--PYRUVATE TRANSAMINASE LEVELS IN LIVERS OF PREGNANT RATS R a t s were k i l l e d on t h e 21 s t or 2 2rid g e s t a t i o n a l d a y (I 2 h p r i o r t o e x p e c t e d p a r t u r i t i o n ) . L i v e r s f r o m 5 p r e g n a n t a n d f r o m 6 n o n p r e g n a n t f e m a l e s were a n a l y z e d . U n i t s of e n z y m e a c t i v i t y are de fi ne d as m / , m o l e s of p r o d u c t f o r m e d p e r rain p e r g of l i v e r s. T h e a v e r a g e w e i g h t s of l i v e r w e re 4-5 a n d 4.1 g p e r i o o g of b o d y w e i g h t for t h e a n i m a l s i n e a c h group. V a l u e s i n c l u d e t h e s t a n d a r d error of t h e mea n.
Age (days)
Pregnant Non-pregnant females
Body weight (g)
Histidi~t,e Histidineammonia-lyase pymvate tran*ami~ase (units per g liver) (units per g liver)
9o-12o
297 4- 8
646 4- 66
9oo -4- 5 o .
IOO-iio
243 4- 6
388 4- 46
666 4- 43
DISCUSSION
The control mechanisms involved in the initiation of the synthesis of specific enzyme proteins in the fetus and newborn remain essentially unknown. I t seems reasonable to assume that more than one factor is involved as there is considerable variation in the times of appearance of various enzymes. The activity of several transaminases in addition to histidine-pyruvate increases at or near parturition; these include t y r o s i n e ~-ketoglutarate transaminase (EC 2.6.1.5) 7 and p h e n y l a l a n i n e - p y r u v a t e and phenylalanine-~-ketoglutarate transaminases 5. A second group of amino acid-catabolizing enzymes appears later; phenylalanine hydroxylase (EC 1.99.1.2 ) becomes measurably active between the 4th and I2th day following parturition 8 and t r y p t o p h a n pyrrolase (EC 1.11.1.4) apparently does not develop to any extent in the rat until some 15 days following birth 9. As histidine ammonia-lyase is barely detectable at birth it would seem to fall in the latter category. It is of interest that enzymes which catalyze consecutive steps of a single p a t h w a y do not necessarily develop at the same time, as observed in the present case in which the development of histidine ammonia-lyase was observed to lag behind that of urocanase. I t is not possible on the basis of available information to assess the relative B i o c h i m . B i o p h y s . A c t a , 9o (1964) 2 8 2 - 2 8 6
286
R. MAKOFF, R. C. BALDRIDGE
amounts of histidine which are degraded by the alternate metabolic pathways at early stages of development. However, it is apparent that histidine-pyruvate transaminase reaches peak activity long before histidase does, and, based upon enzyme activities, the potential for transamination is some 20- or 3o-fold greater than that for straight deamination immediately prior to birth and during the neonatal period. As mentioned previously 6, the intracellular concentrations of pyruvate would undoubtedly be a limiting factor in the amounts of histidine which undergo transamination. The fact that the levels of both histidine ammonia-lyase and of histidinepyruvate transaminase are greater in female than in male rats, coupled with the observation that the levels are higher in pregnant than in non-pregnant females, leads to the suspicion that the activity of both enzymes is related to the estrogen: androgen ratio in the tissues. In recent studies of the sex difference (females > males) in levels of the methionine-methyl activating system, NATORI1° found that the difference was abolished by castration of the male rats and could be restored by administration of androgen. Increased activities of several enzymes in rat liver, e.g., tyrosine transaminase 7, have been noted during pregnancy. Information concerning possible similar changes in the levels of histidine-catabolizing enzymes in the human during pregnancy would be of interest in view of the well-known histidinuria of pregnancy. The original findings of EDLBACHER AND HEITZ11 concerning unchanged "histidase" levels during human pregnancy were based on analyses of autopsy tissue by a non-specific method. ACKNOWLEDGEMENT
This work was supported by Grant No. A65o from the National Institutes of Health, U.S. Public Health Service. REFERENCES 1 A. H. MEHLER AND H. TABOR, J. Biol. Chem., 2Ol (1953) 775. E. V. ROWSELL, Biochem. ]., 64 (1956) 246. 3 V. H. AUERBACH, A. M. DIGEoRGE, R. C. BALDRIDGE, C. D. TOURTELOTTE AND M. P. BRIGHAM, J. Pedlar., 6o (1962) 487 . 4 B. N. LADU, R. R. HOWELL, G. A. JACOBY, J. E. SEEGMILLER AND V. G. ZANNONI, Biochem. Biophys. Res. Commun., 7 (1962) 398. 5 V. H. AUERBACH AND H. WAISMAN, J. Biol. Chem., 234 (1959) 3o4 . 6 p. D. SPOLTER AND R. C. BALDRIDGE, J. Biol. Chem., 238 (1963) 2o71. 7 F. SERENI, F. KENNEY AND N. KRETCHMER, f . Biol. Chem., 234 (1959) 6o9. 8 R. T. KENNEY', G. H. REEM AND N. KRETCHMER, Science, 127 (i958) 86. 9 A. NEMETH, J. Biol. Chem., 234 (1959) 2921. 10 y . NATORI, J. Biol. Chem., 238 (1963) 2075. 11 S. EDLBACHER AND V. L. HEITZ, Z. Physiol. Chem., 276 (1942) 117.
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