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Formation of γ-glutamyl-taurine in the rat brain
Neuroscience Letters, 27 (1981) 145- 149
145
Elsevier/North-Holland Scientific Publishers Ltd.
FORMATION OF 7-GLUTAMYL-TAURINE IN THE RAT BRAIN
KATALIN TOROK, VINCE VARGA, J,~NOS SOMOGYI§, L.~SZLO FEUER* and JOZSEF GULYAS**
Institute of Biochemistry L Semmelweis University Medical School, Budapest (Hungary) *Chinoin Pharmaceutical and Chemical Works Ltd., Budapest (Hungary) and
**Institute of Organic Chemistry, E6tv6s Lordmd University, Budapest (Hungary) (Received August 4th, 1981; Revised version received September 2nd, 1981; Accepted September 14th, 1981)
Key words: brain acidic peptides - 7-glutamyl-taurine - 7-glutamyl transpeptidase
After intraventricular administration of 14C- or 3H-labelled taurine, 3,-glutamyl-taurine was detected in the protein free extract of rat brain using a combination of ion exchange chromatography, electrophoretic separation and thin-layer chromatography. Under in vitro conditions 7-glutamyl-transpeptidase (EC 2.3.2.2.) prepared from rat brain catalyzes the formation of 7-glutamyl-taurine from taurine and glutathione or ~/-glutamyl-p-nitroanilide. The enzymes of the 7-glutamyl cycle are presumed to be responsible for the in vivo metabolism of this dipeptide.
Recent investigations demonstrated that the protein free extract of bovine parathyroidal glands exhibited different biological actions: for example, a retarding effect on the metamorphosis of insects and amphibians; influence on plasma renin activity as well as on exocrine gland dysfunctions; radioprotective effect on the mitotic index of rat bone marrow cells, etc. The active substance of the extract was identified as 3,-glutamyl-taurine [2-7]. This peptide was detected in bovine as well as in salmon muscle and in human blood plasma [11]. On the basis of theoretical considerations [1, 8, 10], we suspected the existence of 7-glutamyl-taurine in the central nervous system. Very recently the presence of a few new peptides in synaptic vesicles has been reported, and one of them is supposed to contain taurine besides aspartic and/or glutamic acids [9]. In the present study the in vivo formation of 7-glutamyl-taurine in the rat brain as well as its in vitro enzymatic synthesis is described. 200 nmol taurine containing 50
§To whom correspondence should be addressed at: Inst. Biochemistry I, Semmelweis University Medical School, Budapest, 8, POB 260, 1444, Hungary. 0304-3940/81/0000-0000/$ 02.75 © Elsevier/North-Holland Scientific Publishers Ltd.
146
lsS q
pH
1000-
-3.O
C m
- ..
~
-2.5
500-
-q El
x..,
10
20
30
-r-
4.5
40 ~.0 froction number
Fig. 1. Ion exchange chromatography of the brain extract. Dowex 1 x 2 (200-400 mesh) column (0.5 x 10 cm) was equilibrated with 0.02 M sodium acetate buffer, pH 2.6. The lyophilized brain extract was applied in a small volume to the column and washed with the same buffer until the free taurine was completely removed. Linear pH gradient (dashed line) was applied for the elution of the bound compounds using a two-chambered reservoir that contained 30 ml each of 0.02 M sodium acetate buffer, pH 2.6, and a mixture of formic acid, acetic acid and water (1:2: 16, by vol.). Radioactivity of the fractions was measured (continuous line). The elution of standard amino acids and y-glutamyl-taurine (purchased from Chinoin Pharm. Works, Budapest, Hungary, purity 99%) is indicated below the chromatogram. #Ci [1,2-14C]taurine (56 m C i / m m o l , New E n g l a n d Nuclear) o r 10 #Ci [1-3H]taurine (9 C i / m m o l , T h e R a d i o c h e m i c a l Centre, A m e r s h a m ) in 0.85°7o N a C I has been injected i n t r a v e n t r i c u l a r l y to n a r c o t i z e d rats for 5 min. A f t e r 30 m i n the rats were d e c a p i t a t e d , the b r a i n s were r a p i d l y r e m o v e d a n d h o m o g e n i z e d in 10 vol. o f ice-cold 5o70 ( v / v ) acetic acid. T h e h o m o g e n a t e was c e n t r i f u g e d at 2000 x g for 30 min a n d the pellet was w a s h e d twice with 5o70 acetic acid. T h e c o m b i n e d s u p e r n a t a n t was l y o p h i l i z e d a n d f r a c t i o n a t e d by ion exchange c h r o m a t o g r a p h y as d e s c r i b e d in Fig. 1. A f t e r r e m o v i n g free t a u r i n e a single large r a d i o a c t i v e p e a k was o b s e r v e d in the eluate c o r r e s p o n d i n g to the elution o f 3,-glutamyl-taurine (Fig. 1). T h e r a d i o a c t i v e f r a c t i o n s were c o m b i n e d a n d lyophilized. T h e i d e n t i t y o f the r a d i o a c t i v e c o m p o u n d was c o n f i r m e d by e l e c t r o p h o r e t i c a n d c h r o m a t o g r a p h i c analysis. In c o n t r a s t to the ion e x c h a n g e c h r o m a t o g r a p h y , two r a d i o a c t i v e spots were f o u n d in p a p e r electrop h o r e t o g r a m s as well as in thin layer c h r o m a t o g r a m s . T h e r a d i o a c t i v e spots were eluted with distilled water f r o m the p a p e r as well as f r o m the thin layer a n d h y d r o l y z e d at 105 °C with 5.5 M H C I for 24 h. T h e only r a d i o a c t i v e c o m p o u n d detected in the h y d r o l y z a t e s by T L C was i d e n t i f i e d as taurine.
147 TABLE I R E L A T I V E E L E C T R O P H O R E T I C MOBILITIES A N D R: VALUES OF R A D I O A C T I V E S A M P L E S P R E P A R E D F R O M BRAIN AS W E L L AS T H O S E OF C O N T R O L S C O M P O U N D S Paper electrophoresis of the c o m p o u n d s investigated was carried out using W h a t m a n l chromatographic paper at 32 V / c m in formic acid:acetic acid:water ( 1 : 4 : 4 5 , by vol.) at p H 1.9, in acetic acid : pyridine: water (10:1:89, by vol.) at pH 4.4, and in acetic acid : pyridine :water (1 : 11 : 100, by vol.) at pH 6.5 for 1-3 h using a cooled plate equipment. The relative electrophoretic mobilities of the c o m p o u n d s investigated were calculated as compared to cysteine sulfonic acid. Thin layer chromatography was carried out with cellulose plates (pre-coated TLC plates Merck, F.R.G.) in methanol:pyridine :water (20:1 : 5 by vol.) ('A'), and in n-butanol: pyridine:acetic acid :water (15 : 10 : 3 : 12, by vol. ('B').
Rf values in
Relative mobilities in paper electrophoretograms
TLC
pH 1.9
pH 3.5
pH 4.4
pH 6.5
'A'
'B'
Labelled C o m p o u n d 1 7-Glutamyl-taurine a-Glutamyl-taurine Taurine a-Aspartyl-taurine j3-Aspartyl-taurine
0.52 0.52 0 0 0 0.52
0.73 0.72 0 0.52 0.80
0.72 0.72 0 0.68 0.80
0.72 0.72 0.72 0 0.80 0.80
0.67 0.67 0.73 0.61 0.50
0.18 0.18 0.31 0.16
Labelled C o m p o u n d lI Cysteic acid
1.0 1.0
1.0 1.0
1.0 1.0
1.0 1.0
0.38 0.52
One of the compounds containing labelled taurine proved to be identical with -y-glutamyl-taurine considering its relative electrophoretic mobility and chromatographic Rf value (Table I). The Rf values as well as the relative electrophoretic mobility of ~-aspartyl-taurine (received from A. Horv~th) have been found to differ from those of -r-glutamyl-taurine. c~-Aspartyl-taurine and a-glutamyltaurine could likewise be excluded because they do not move away from the starting point at pH 1.9. The other radioactive compound has not yet been identified exactly. This unidentified compound containing taurine probably has no free amino group since it does not react with 1-fluoro-2,4-dinitrobenzene. Its mobility as determined by paper electrophoresis is the same as that of cysteic acid, but its chromatographic properties are different from those of cysteic acid. On the basis of its mobility the unidentified compound does not seem to be identical with any of N-methyl-taurine, N-acetyl-taurine, pyro-glutamyl-taurine, isethionic acid or taurocholic acid. Neither labelled glutamyl-ditaurine, aspartyl-ditaurine, "r-glutamyl-7-glutamyl-taurine nor cysteic acid were detected in our experiments. After the intraventricular administration of labelled taurine approximately a 1/10,000 part of the injected amount was detected as ~-glutamyl-taurine and another not identified compound.
148 T A B L E 11 IDENTIFICATION OF 7 - G L U T A M Y L - T A U R I N E S Y N T H E T I Z E D FROM G L U T A T H I O N E A N D T A U R I N E BY 7 - G L U T A M Y L - T R A N S P E P T I D A S E ?-Glutamyl-transpeptidase was prepared from rat brain including a purification step by affinity chromatography essentially as described by Tare and Meister [12]. The medium contained 0.1 M Tris-Cl buffer pH 8.2, 0.15 M NaCI, I0 m M MgC12, either 5 m M -y-glutamyl-p-nitroanilide or 5 mM glutathione-SH as 3,-glutamyl donor, 20-50 m M taurine and 3,-glutamyl-transpeptidase (50/zg protein) m 0.5 ml. After incubation at 37 °C for 30-60 min the reaction was stopped by addition of 1.0 ml 3 M acetic acid. The ~t-glutamyl-taurine was detected in the lyophilized protein free supernatant by paper etectrophoresis (as described in Table 1). Descendent paper chromatography was carried out using W h a t m a n 1 paper in n-butanol:pyridine:acetic acid:water ( 1 5 : 1 0 : 3 : 1 , by vol.) ('C') for 60 h. Relative electrophoretic mobilities were calculated as in "Fable 1, and the relative chromatographic mobility was calculated as compared to glutamic acid. Relative mobilities
Sample or 7-glutamyl-taurine
Paper electrophoretogram
Paper chromatogram
pH 1.9
pH 3.5
pH 6.5
solvent ' C '
0.52
0.72
0.72
0.83
To control for the possibility that the 7-glutamyl-taurine formed in vivo from labelled taurine was synthetized by 7-glutamyl-transpeptidase of the brain, taurine was incubated with glutathione or with 3,-glutamyl-p-nitroanilide in the presence of a partially purified 3,-glutamyl-transpeptidase [12]. The compounds formed were detected in the protein free extract of the reaction mixture using several electrophoretic and chromatographic systems. Beside other ~,-glutamyl-compounds, 3,-glutamyl-taurine was also detected (Table II), supporting the hypothesis that 7-glutamyl-taurine, which can be formed under in vivo conditions, may be the product of 7-glutamyl-transpeptidase. During the last decade different 3,-glutamyl peptides have been found in the nervous system. Although their role remains to be clarified, the fact that these acidic peptides are not detectable in other tissues, or only in extremly low concentrations, indicates that they may have some specific neurochemical functions. This conception refers to 3,-glutamyl-taurine too. The only enzyme known to catalyze 7glutamyl transpeptidation is 3,-glutamyl-transpeptidase. It is able not only to synthetize 7-glutamyl-taurine, but under certain conditions the enzyme may use it as a 7glutamyl donor for other transpeptidations too. Beside -y-glutamyl-transpeptidase the 3,-glutamyl-cyclotransferase (EC 2.3.2.4.) can be supposed to have the main role in the biodegradation of ~,-glutamyl-taurine. The relative activities of the two enzymes are quite different in the various areas of the central nervous system [13], supporting the idea that the ratio of these two enzymes might determine the actual concentration of 7-glutamyl-taurine in the different regions of the brain. The validity of this hypothesis remains to be demonstrated.
149 1 Feuer, L., Theoretical background of the recognition of a new bioactive substance, Litoralon, isolated from the parathyroid. Further theoretical considerations, Biologia, 25 (1977) 3-33. 2 Feuer, L., B~nyai, B. and Hercsel, J., Influence of protein free aqueous extract of parathyroid powder on serum vitamin A level in rats, Experientia, 33 (1977) 1005-1006. 3 Feuer, L., Furka, A., Sebesty~n, F., Hercsel, J. and Bendefy, E., Taurine derivative and its isolation, British Path., 1 (1978) 503-674. 4 Feuer, L. and GaAl, K., Effect of glutaurine on plasma renin activity in the rat and the dog, Gen. comp. Endocr., 39 (1979) 330-335. 5 Feuer, L. and Ormai, S., Radioprotective effect of a protein free parathyroid extract on the mitotic index of rat bone marrow cells, Experientia, 35 (1979) 1091-1092. 6 Feuer, L., TOr0k, L.J., Kapa, E. and Csaba, G., The effect of -r-glutamyl-taurine on the amphibian metamorphosis, Comp. Biochem. Physiol., 61 (1978) 67-71. 7 Furka, A., Sebesty~n, F., Feuer, L., Horvath, A., Hercsel, J., Ormai, S. and Banyai, B., Isolation of -r-L-glutamyl-taurine from the protein free aqueous extract of bovine parathyroid powder, Acta biochim, biophys, hung., 15 (1980) 39-47. 8 Konishi, H. and Kakimoto, Y., Formation of 3~-glutamyl-histamine from histamine in rat brain, J. Neurochem., 27 (1976) 1461-1463. 9 Lahdesmaki, P., Airaksinen, K., Vartiainen, M. and Halonen, P., Characterization of two synaptosomal peptides in calf brain, Acta chem. scand., B, 34 (1980) 343-348. 10 Reichelt, K.L., The isolation of gamma-glutamyl peptides from monkey brain, J. Neurochem., 17 (1970) 19-25. 11 Sebesty~n, P., Gonda, A., Horv~tth, A., Szbk~m, Gy., Furka, A., Feuer, L. and Path, J., Presence of 3,-L-glutamyl-taurine in bovine as well as salmon muscle and human blood plasma, Experientia, in press. 12 Tate, S.S. and Meister, A., Identity of maleate-stimulated glutaminase with 3,-glutamyl transpeptidase in rat kidney, J. biol. Chem., 250 (1974) 4619-4624. 13 Tsuji, M., Matsuoka, Y. and Nakajima, T., Studies on formation of ~,-glutamylamines in rat brain and their synthetic and catabolic enzymes, J. Neurochem., 29 (1977) 633-638.
145
Elsevier/North-Holland Scientific Publishers Ltd.
FORMATION OF 7-GLUTAMYL-TAURINE IN THE RAT BRAIN
KATALIN TOROK, VINCE VARGA, J,~NOS SOMOGYI§, L.~SZLO FEUER* and JOZSEF GULYAS**
Institute of Biochemistry L Semmelweis University Medical School, Budapest (Hungary) *Chinoin Pharmaceutical and Chemical Works Ltd., Budapest (Hungary) and
**Institute of Organic Chemistry, E6tv6s Lordmd University, Budapest (Hungary) (Received August 4th, 1981; Revised version received September 2nd, 1981; Accepted September 14th, 1981)
Key words: brain acidic peptides - 7-glutamyl-taurine - 7-glutamyl transpeptidase
After intraventricular administration of 14C- or 3H-labelled taurine, 3,-glutamyl-taurine was detected in the protein free extract of rat brain using a combination of ion exchange chromatography, electrophoretic separation and thin-layer chromatography. Under in vitro conditions 7-glutamyl-transpeptidase (EC 2.3.2.2.) prepared from rat brain catalyzes the formation of 7-glutamyl-taurine from taurine and glutathione or ~/-glutamyl-p-nitroanilide. The enzymes of the 7-glutamyl cycle are presumed to be responsible for the in vivo metabolism of this dipeptide.
Recent investigations demonstrated that the protein free extract of bovine parathyroidal glands exhibited different biological actions: for example, a retarding effect on the metamorphosis of insects and amphibians; influence on plasma renin activity as well as on exocrine gland dysfunctions; radioprotective effect on the mitotic index of rat bone marrow cells, etc. The active substance of the extract was identified as 3,-glutamyl-taurine [2-7]. This peptide was detected in bovine as well as in salmon muscle and in human blood plasma [11]. On the basis of theoretical considerations [1, 8, 10], we suspected the existence of 7-glutamyl-taurine in the central nervous system. Very recently the presence of a few new peptides in synaptic vesicles has been reported, and one of them is supposed to contain taurine besides aspartic and/or glutamic acids [9]. In the present study the in vivo formation of 7-glutamyl-taurine in the rat brain as well as its in vitro enzymatic synthesis is described. 200 nmol taurine containing 50
§To whom correspondence should be addressed at: Inst. Biochemistry I, Semmelweis University Medical School, Budapest, 8, POB 260, 1444, Hungary. 0304-3940/81/0000-0000/$ 02.75 © Elsevier/North-Holland Scientific Publishers Ltd.
146
lsS q
pH
1000-
-3.O
C m
- ..
~
-2.5
500-
-q El
x..,
10
20
30
-r-
4.5
40 ~.0 froction number
Fig. 1. Ion exchange chromatography of the brain extract. Dowex 1 x 2 (200-400 mesh) column (0.5 x 10 cm) was equilibrated with 0.02 M sodium acetate buffer, pH 2.6. The lyophilized brain extract was applied in a small volume to the column and washed with the same buffer until the free taurine was completely removed. Linear pH gradient (dashed line) was applied for the elution of the bound compounds using a two-chambered reservoir that contained 30 ml each of 0.02 M sodium acetate buffer, pH 2.6, and a mixture of formic acid, acetic acid and water (1:2: 16, by vol.). Radioactivity of the fractions was measured (continuous line). The elution of standard amino acids and y-glutamyl-taurine (purchased from Chinoin Pharm. Works, Budapest, Hungary, purity 99%) is indicated below the chromatogram. #Ci [1,2-14C]taurine (56 m C i / m m o l , New E n g l a n d Nuclear) o r 10 #Ci [1-3H]taurine (9 C i / m m o l , T h e R a d i o c h e m i c a l Centre, A m e r s h a m ) in 0.85°7o N a C I has been injected i n t r a v e n t r i c u l a r l y to n a r c o t i z e d rats for 5 min. A f t e r 30 m i n the rats were d e c a p i t a t e d , the b r a i n s were r a p i d l y r e m o v e d a n d h o m o g e n i z e d in 10 vol. o f ice-cold 5o70 ( v / v ) acetic acid. T h e h o m o g e n a t e was c e n t r i f u g e d at 2000 x g for 30 min a n d the pellet was w a s h e d twice with 5o70 acetic acid. T h e c o m b i n e d s u p e r n a t a n t was l y o p h i l i z e d a n d f r a c t i o n a t e d by ion exchange c h r o m a t o g r a p h y as d e s c r i b e d in Fig. 1. A f t e r r e m o v i n g free t a u r i n e a single large r a d i o a c t i v e p e a k was o b s e r v e d in the eluate c o r r e s p o n d i n g to the elution o f 3,-glutamyl-taurine (Fig. 1). T h e r a d i o a c t i v e f r a c t i o n s were c o m b i n e d a n d lyophilized. T h e i d e n t i t y o f the r a d i o a c t i v e c o m p o u n d was c o n f i r m e d by e l e c t r o p h o r e t i c a n d c h r o m a t o g r a p h i c analysis. In c o n t r a s t to the ion e x c h a n g e c h r o m a t o g r a p h y , two r a d i o a c t i v e spots were f o u n d in p a p e r electrop h o r e t o g r a m s as well as in thin layer c h r o m a t o g r a m s . T h e r a d i o a c t i v e spots were eluted with distilled water f r o m the p a p e r as well as f r o m the thin layer a n d h y d r o l y z e d at 105 °C with 5.5 M H C I for 24 h. T h e only r a d i o a c t i v e c o m p o u n d detected in the h y d r o l y z a t e s by T L C was i d e n t i f i e d as taurine.
147 TABLE I R E L A T I V E E L E C T R O P H O R E T I C MOBILITIES A N D R: VALUES OF R A D I O A C T I V E S A M P L E S P R E P A R E D F R O M BRAIN AS W E L L AS T H O S E OF C O N T R O L S C O M P O U N D S Paper electrophoresis of the c o m p o u n d s investigated was carried out using W h a t m a n l chromatographic paper at 32 V / c m in formic acid:acetic acid:water ( 1 : 4 : 4 5 , by vol.) at p H 1.9, in acetic acid : pyridine: water (10:1:89, by vol.) at pH 4.4, and in acetic acid : pyridine :water (1 : 11 : 100, by vol.) at pH 6.5 for 1-3 h using a cooled plate equipment. The relative electrophoretic mobilities of the c o m p o u n d s investigated were calculated as compared to cysteine sulfonic acid. Thin layer chromatography was carried out with cellulose plates (pre-coated TLC plates Merck, F.R.G.) in methanol:pyridine :water (20:1 : 5 by vol.) ('A'), and in n-butanol: pyridine:acetic acid :water (15 : 10 : 3 : 12, by vol. ('B').
Rf values in
Relative mobilities in paper electrophoretograms
TLC
pH 1.9
pH 3.5
pH 4.4
pH 6.5
'A'
'B'
Labelled C o m p o u n d 1 7-Glutamyl-taurine a-Glutamyl-taurine Taurine a-Aspartyl-taurine j3-Aspartyl-taurine
0.52 0.52 0 0 0 0.52
0.73 0.72 0 0.52 0.80
0.72 0.72 0 0.68 0.80
0.72 0.72 0.72 0 0.80 0.80
0.67 0.67 0.73 0.61 0.50
0.18 0.18 0.31 0.16
Labelled C o m p o u n d lI Cysteic acid
1.0 1.0
1.0 1.0
1.0 1.0
1.0 1.0
0.38 0.52
One of the compounds containing labelled taurine proved to be identical with -y-glutamyl-taurine considering its relative electrophoretic mobility and chromatographic Rf value (Table I). The Rf values as well as the relative electrophoretic mobility of ~-aspartyl-taurine (received from A. Horv~th) have been found to differ from those of -r-glutamyl-taurine. c~-Aspartyl-taurine and a-glutamyltaurine could likewise be excluded because they do not move away from the starting point at pH 1.9. The other radioactive compound has not yet been identified exactly. This unidentified compound containing taurine probably has no free amino group since it does not react with 1-fluoro-2,4-dinitrobenzene. Its mobility as determined by paper electrophoresis is the same as that of cysteic acid, but its chromatographic properties are different from those of cysteic acid. On the basis of its mobility the unidentified compound does not seem to be identical with any of N-methyl-taurine, N-acetyl-taurine, pyro-glutamyl-taurine, isethionic acid or taurocholic acid. Neither labelled glutamyl-ditaurine, aspartyl-ditaurine, "r-glutamyl-7-glutamyl-taurine nor cysteic acid were detected in our experiments. After the intraventricular administration of labelled taurine approximately a 1/10,000 part of the injected amount was detected as ~-glutamyl-taurine and another not identified compound.
148 T A B L E 11 IDENTIFICATION OF 7 - G L U T A M Y L - T A U R I N E S Y N T H E T I Z E D FROM G L U T A T H I O N E A N D T A U R I N E BY 7 - G L U T A M Y L - T R A N S P E P T I D A S E ?-Glutamyl-transpeptidase was prepared from rat brain including a purification step by affinity chromatography essentially as described by Tare and Meister [12]. The medium contained 0.1 M Tris-Cl buffer pH 8.2, 0.15 M NaCI, I0 m M MgC12, either 5 m M -y-glutamyl-p-nitroanilide or 5 mM glutathione-SH as 3,-glutamyl donor, 20-50 m M taurine and 3,-glutamyl-transpeptidase (50/zg protein) m 0.5 ml. After incubation at 37 °C for 30-60 min the reaction was stopped by addition of 1.0 ml 3 M acetic acid. The ~t-glutamyl-taurine was detected in the lyophilized protein free supernatant by paper etectrophoresis (as described in Table 1). Descendent paper chromatography was carried out using W h a t m a n 1 paper in n-butanol:pyridine:acetic acid:water ( 1 5 : 1 0 : 3 : 1 , by vol.) ('C') for 60 h. Relative electrophoretic mobilities were calculated as in "Fable 1, and the relative chromatographic mobility was calculated as compared to glutamic acid. Relative mobilities
Sample or 7-glutamyl-taurine
Paper electrophoretogram
Paper chromatogram
pH 1.9
pH 3.5
pH 6.5
solvent ' C '
0.52
0.72
0.72
0.83
To control for the possibility that the 7-glutamyl-taurine formed in vivo from labelled taurine was synthetized by 7-glutamyl-transpeptidase of the brain, taurine was incubated with glutathione or with 3,-glutamyl-p-nitroanilide in the presence of a partially purified 3,-glutamyl-transpeptidase [12]. The compounds formed were detected in the protein free extract of the reaction mixture using several electrophoretic and chromatographic systems. Beside other ~,-glutamyl-compounds, 3,-glutamyl-taurine was also detected (Table II), supporting the hypothesis that 7-glutamyl-taurine, which can be formed under in vivo conditions, may be the product of 7-glutamyl-transpeptidase. During the last decade different 3,-glutamyl peptides have been found in the nervous system. Although their role remains to be clarified, the fact that these acidic peptides are not detectable in other tissues, or only in extremly low concentrations, indicates that they may have some specific neurochemical functions. This conception refers to 3,-glutamyl-taurine too. The only enzyme known to catalyze 7glutamyl transpeptidation is 3,-glutamyl-transpeptidase. It is able not only to synthetize 7-glutamyl-taurine, but under certain conditions the enzyme may use it as a 7glutamyl donor for other transpeptidations too. Beside -y-glutamyl-transpeptidase the 3,-glutamyl-cyclotransferase (EC 2.3.2.4.) can be supposed to have the main role in the biodegradation of ~,-glutamyl-taurine. The relative activities of the two enzymes are quite different in the various areas of the central nervous system [13], supporting the idea that the ratio of these two enzymes might determine the actual concentration of 7-glutamyl-taurine in the different regions of the brain. The validity of this hypothesis remains to be demonstrated.
149 1 Feuer, L., Theoretical background of the recognition of a new bioactive substance, Litoralon, isolated from the parathyroid. Further theoretical considerations, Biologia, 25 (1977) 3-33. 2 Feuer, L., B~nyai, B. and Hercsel, J., Influence of protein free aqueous extract of parathyroid powder on serum vitamin A level in rats, Experientia, 33 (1977) 1005-1006. 3 Feuer, L., Furka, A., Sebesty~n, F., Hercsel, J. and Bendefy, E., Taurine derivative and its isolation, British Path., 1 (1978) 503-674. 4 Feuer, L. and GaAl, K., Effect of glutaurine on plasma renin activity in the rat and the dog, Gen. comp. Endocr., 39 (1979) 330-335. 5 Feuer, L. and Ormai, S., Radioprotective effect of a protein free parathyroid extract on the mitotic index of rat bone marrow cells, Experientia, 35 (1979) 1091-1092. 6 Feuer, L., TOr0k, L.J., Kapa, E. and Csaba, G., The effect of -r-glutamyl-taurine on the amphibian metamorphosis, Comp. Biochem. Physiol., 61 (1978) 67-71. 7 Furka, A., Sebesty~n, F., Feuer, L., Horvath, A., Hercsel, J., Ormai, S. and Banyai, B., Isolation of -r-L-glutamyl-taurine from the protein free aqueous extract of bovine parathyroid powder, Acta biochim, biophys, hung., 15 (1980) 39-47. 8 Konishi, H. and Kakimoto, Y., Formation of 3~-glutamyl-histamine from histamine in rat brain, J. Neurochem., 27 (1976) 1461-1463. 9 Lahdesmaki, P., Airaksinen, K., Vartiainen, M. and Halonen, P., Characterization of two synaptosomal peptides in calf brain, Acta chem. scand., B, 34 (1980) 343-348. 10 Reichelt, K.L., The isolation of gamma-glutamyl peptides from monkey brain, J. Neurochem., 17 (1970) 19-25. 11 Sebesty~n, P., Gonda, A., Horv~tth, A., Szbk~m, Gy., Furka, A., Feuer, L. and Path, J., Presence of 3,-L-glutamyl-taurine in bovine as well as salmon muscle and human blood plasma, Experientia, in press. 12 Tate, S.S. and Meister, A., Identity of maleate-stimulated glutaminase with 3,-glutamyl transpeptidase in rat kidney, J. biol. Chem., 250 (1974) 4619-4624. 13 Tsuji, M., Matsuoka, Y. and Nakajima, T., Studies on formation of ~,-glutamylamines in rat brain and their synthetic and catabolic enzymes, J. Neurochem., 29 (1977) 633-638.