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Comparative aspects of incorporation of vanadium, tungsten or molybdenum into protein of nitrate reductase of Spinacea oleracea L. leaves
355
BIOCHIMICA ET BIOPHYSICA ACTA
BBA
46349
COMPARATIVE ASPECTS OF INCORPORATION OF VANADIUM, TUNGSTEN OR MOLYBDENUM INTO P R O T E I N OF N I T R A T E REDUCTASE OF S P I N A C E A
O L E R A C E A L. LEAVES
B. A. N O T T O N AND E. J. H E \ V I T T
Long A shton Research Station, University of Bristol, Long ,4 shto~L Bristol, BSI8 9AF (Great Britain) (l~eceived March 27th, 1972)
SUMMARY
Spinach was grown in molybdenum-deficient sand culture, given radioactively labelled molybdenum, tungsten or vanadium and the protein fractionated for nitrate reduetase. Enzymatically active nitrate reductase was formed with molybdenum but not tungsten. Both molybdenum and tungsten were incorporated into protein associated with nitrate reductase or similar but inert protein. Vanadium was not incorporated into any protein and did not promote nitrate reductase activity. Vanadium tended to accumulate in the roots and unlike molybdenum or tungsten was not freely translocated to the leaves.
The specific association between Mo and N assimilation by N 2 fixation or NO 3reduction is firmly established x, 2. The metal is a tightly bound prosthetic component of the proteins in both systems. V can substitute for Mo in N 2 fixation by certain species of A zotobacter 3. The substitution of V for Mo in a growth medium for A zotobacter vindandii OP cells4, 5 resulted in the isolation of protein in the purified nitrogenase fraction having a ratio of 93 % V to Mo and decreased specific activity, binding affinity for acetylene and stability to heat. In contrast, V is unable to modify the Mo requirement of a blue-green alga Anabaena e, or in legume root nodules v. W is an antagonist of Mo in N~ fixation and NO 3- assimilation by Azotobacter, but V appears unable to reverse antagonism by WOsS, 9. Inhibition by W of the formation of nitrate reductase activity by Mo in suspended cultures of tobacco XD cells and in intact barley seedlings TM was shown in spinach n to be the formation of an enzymatically inactive W analogue of the enzyme in which it is resistant to removal by dialysis with cyanide or exchange with Mo TM. It therefore seemed pertinent to test for the possible formation of a V analogue using the same technique. In the first experiment, Mo-deficient spinach plants were grown as previously described 13 for 6 weeks before being supplied with 200 ml of Mo-free nutrient solution containing I0/~Ci 49V and 200/~g V as VO 3. After 24 h the leaves were sampled and extracted protein was purified as for nitrate reductase TM. There was a continual loss of radioactivity during enzyme purification from the initially low level of 324 counts/ IOOO s per g fresh wt to zero (background level) in the most purified extract in which the specific activity of the initially low nitrate reductase had increased 25 times. The Biochirn. Biophys. Acta, 275 (1972) 355-357
356
B.A.
N O T T O N , E. J . H E W I T T
radioactivity of the roots, well washed with VO 3 solution to remove extraneous 49V, was 13965 counts/Iooo s per g fresh wt confirming previous observations on the accumulation of V in the roots of higher plants ~4, ~5. TABLE
I
COMPARISON I~ETWEEN ACCUMULATION IN PROTEIN FRACTIONS NORMALLY RICH IN NITRATE REDUCTASE OF V, \ ¥ AND ~'Io \VHEN ADDED TO ~]O-DEFICIENT SPINACH PLANTS N i t r a t e r e d u e t a s e a c t i v i t y ( N . R . ) e x p r e s s e d as n m o l e s N O , 2 p r o d u c e d / 1 5 m i n p e r nag p r o t e i u . R a d i o a c t i v i t y (49V, t s ~ \ v a n d °gMo) e x p r e s s e d a s c o u n t s / i o o o s p e r m g p r o t e i n . Fractiou
Treatment :
Cell-free extract C a 3 ( P O , ) ~ gel e l u a t e 0-50o/0 (NH4)2SO 4 precipitate Alumina c7 eluate
-- 3f0
1"
N.R.
49V
8. 4
51 21 14 o
57.7
75.6 19I
- Mo
W
-- Mo
Mo
N.R.
assW
N.R.
99M0
io.2 73.4 92. 5 245
~24 o 5331 5511 18632
12 174 208 421
572t 4607 4937 10228
In the second experiment the carrier V was decreased to 40 /zg in 200 ml of Mo-free nutrient solution containing 9 #Ci 49V and the plants were left for 48 h before sampling. This treatment led to a 3-fold increase in the foliar V to 944 counts/Iooo s per g fresh wt. Table I shows the subsequent purification of nitrate reductase with corresponding radioactivity from these plants compared with effects of equivalent doses of W and Mo given under similar conditions. It is seen that whereas W and Mo accumulate in the fractions rich in nitrate reductase V becomes progressively diluted out. The increase in specific activity of the enzyme during purification was similar for V and W treatments (24 ×) but higher for Mo treatment (35 ×) which has a greater level of enzyme activity due to the inductive effect of Mo. Pre- and posttreatment levels of enzyme activity (nmoles NO 2 produced/I 5 min per g fresh wt) were 164 and 155 for V, 18o and 149 for W, and lO2 and 334 for Mo. In no case did the enzyme activity of the leaves significantly increase as a result of treatment with V. It was therefore clear that no biosynthetically produced V analogue of nitrate reductase was formed under these conditions. This contrasted with W, which induces an enzymically inactive protein 11 and with Mo which is the natural prosthetic metal of the enzyme 13. The atomic radii of the three metals are 1.29, 1.3o and 1.22 for No, W and V, respectively, and the ionic radii of the M4+ state are o.68, o.68 and o.6416 suggesting that the inability of V to form an analogue is related to its size. By analogy, the inability of the W analogue to be enzymically active does not result from altered spatial relationships with the protein but from some other factor, possibly redox potential. Available information 1~ shows W to differ significantly from Mo in several redox systems. The results also suggest that nitrate reductase is less flexible around the Mo site of the protein than nitrogenase. In the latter, a V-containing analogue either shows functional but modified properties or a V-containing protein of similar purification characteristics is produced which influences the activity of diminished amounts of nitrogenase. V shows no affinity with nitrate reductase as it is neither incorporated into, nor seems to modify, residual nitrate reductase protein. lgiochim,
lCiophys. A c l a , 275 (1972) 3 5 5 - 3 5 7
INCORPORATION OF V , W OR M o INTO NITRATE REDUCTASE
357
ACKNOWLEDGEMENTS
We would like to thank Mr C. P. Lloyd-Jones for automated counting facilities, Mr E. F. Watson for growing the plants, and Mr R. J. Fido for technical assistance during this investigation. REFERENCES I J. R. P o s t g a t e , The Chemistry and Biochemistry of Nitrogen Fixation, P l e n u m Press, L o n d o n , I97 I, p. 191 . 2 E. J. H e w i t t a n d D. J. D. Nicholas, in H. F. Linsken, t3. D. Sanwall a n d M. V. Tracey, Modern Methods of Plant Analysis, Vol. 7, Springer, Berlin, 1964, p. 67. 3 J- H. Becking, Plant and Soil, 16 (1962) 171. 4 C. E. M c K e n n a , J. R. B e n e m a n n a n d T. G. Taylor, Biochem. Biophys. Res. Commun., 41 (197 o) I5OI. 5 R. C. B u r n s , W. H. F u c h s m a n a n d R. \V. F. H a r d y , Biochem. Biophys. Res. Commun., 42 (197 I) 353. 6 M. B. Allan, Sci. Mon., 83 (I956) lOO. 7 H. C. J e n s o n a n d R. C. B e t t y , Proc. Linn. Soc. N.S. Wales, 68 (1943) 1. 8 H. T a k a h a s h i a n d A. Nason, Biochim. Biophys. Acta, 23 (1957) 433. 9 R. F. Keeler a n d J. E. Varner, Arch. Biochem. Biophys., 7 ° (1957) 585 • IO Y. M. H e i m e r , J. L. W r a y a n d P. Filner, Plant Physiol., 44 (I969) I197. 1i B. A. N o t t o n a n d E. J. H e w i t t , Biochem. Biophys. Res. Commun., 44 (1971) 7 o2. 12 B. A. N o r t o n a n d E. J. Hewitt, F E B S Lett., I8 (i971) I9. 13 13. A. N o r t o n a n d E. J. H e w i t t , Plant Cell Physiol., i2 (1971) 465. 14 D. B e r t r a n d , Ann. Inst. Pasteur, 68 (I94e) 58. t 5 E. J. H e w i t t , Sand and Water Culture Methods used in the study of Plant Nutrition, C o m m o n w e a l t h B u r e a u of H o r t i c u l t u r e , Tech. C o m m u n . 22, F a r n h a m Royal, E n g l a n d , 2 n d edn, 1966, p. 176. 16 R. B. Heslop a n d P. L. R o b i n s o n , Inorganic Chemistry, Elsevier, A m s t e r d a m , 196o. 17 C. D. H o d g m a n , Handbooh of Chemistry and Physics, T h e Chemical R u b b e r C o m p a n y P u b lishing C o m p a n y , Cleveland, Ohio, 43rd edn, 1961.
Biochim. Biophys. Acta, 275 (1972) 355-357
BIOCHIMICA ET BIOPHYSICA ACTA
BBA
46349
COMPARATIVE ASPECTS OF INCORPORATION OF VANADIUM, TUNGSTEN OR MOLYBDENUM INTO P R O T E I N OF N I T R A T E REDUCTASE OF S P I N A C E A
O L E R A C E A L. LEAVES
B. A. N O T T O N AND E. J. H E \ V I T T
Long A shton Research Station, University of Bristol, Long ,4 shto~L Bristol, BSI8 9AF (Great Britain) (l~eceived March 27th, 1972)
SUMMARY
Spinach was grown in molybdenum-deficient sand culture, given radioactively labelled molybdenum, tungsten or vanadium and the protein fractionated for nitrate reduetase. Enzymatically active nitrate reductase was formed with molybdenum but not tungsten. Both molybdenum and tungsten were incorporated into protein associated with nitrate reductase or similar but inert protein. Vanadium was not incorporated into any protein and did not promote nitrate reductase activity. Vanadium tended to accumulate in the roots and unlike molybdenum or tungsten was not freely translocated to the leaves.
The specific association between Mo and N assimilation by N 2 fixation or NO 3reduction is firmly established x, 2. The metal is a tightly bound prosthetic component of the proteins in both systems. V can substitute for Mo in N 2 fixation by certain species of A zotobacter 3. The substitution of V for Mo in a growth medium for A zotobacter vindandii OP cells4, 5 resulted in the isolation of protein in the purified nitrogenase fraction having a ratio of 93 % V to Mo and decreased specific activity, binding affinity for acetylene and stability to heat. In contrast, V is unable to modify the Mo requirement of a blue-green alga Anabaena e, or in legume root nodules v. W is an antagonist of Mo in N~ fixation and NO 3- assimilation by Azotobacter, but V appears unable to reverse antagonism by WOsS, 9. Inhibition by W of the formation of nitrate reductase activity by Mo in suspended cultures of tobacco XD cells and in intact barley seedlings TM was shown in spinach n to be the formation of an enzymatically inactive W analogue of the enzyme in which it is resistant to removal by dialysis with cyanide or exchange with Mo TM. It therefore seemed pertinent to test for the possible formation of a V analogue using the same technique. In the first experiment, Mo-deficient spinach plants were grown as previously described 13 for 6 weeks before being supplied with 200 ml of Mo-free nutrient solution containing I0/~Ci 49V and 200/~g V as VO 3. After 24 h the leaves were sampled and extracted protein was purified as for nitrate reductase TM. There was a continual loss of radioactivity during enzyme purification from the initially low level of 324 counts/ IOOO s per g fresh wt to zero (background level) in the most purified extract in which the specific activity of the initially low nitrate reductase had increased 25 times. The Biochirn. Biophys. Acta, 275 (1972) 355-357
356
B.A.
N O T T O N , E. J . H E W I T T
radioactivity of the roots, well washed with VO 3 solution to remove extraneous 49V, was 13965 counts/Iooo s per g fresh wt confirming previous observations on the accumulation of V in the roots of higher plants ~4, ~5. TABLE
I
COMPARISON I~ETWEEN ACCUMULATION IN PROTEIN FRACTIONS NORMALLY RICH IN NITRATE REDUCTASE OF V, \ ¥ AND ~'Io \VHEN ADDED TO ~]O-DEFICIENT SPINACH PLANTS N i t r a t e r e d u e t a s e a c t i v i t y ( N . R . ) e x p r e s s e d as n m o l e s N O , 2 p r o d u c e d / 1 5 m i n p e r nag p r o t e i u . R a d i o a c t i v i t y (49V, t s ~ \ v a n d °gMo) e x p r e s s e d a s c o u n t s / i o o o s p e r m g p r o t e i n . Fractiou
Treatment :
Cell-free extract C a 3 ( P O , ) ~ gel e l u a t e 0-50o/0 (NH4)2SO 4 precipitate Alumina c7 eluate
-- 3f0
1"
N.R.
49V
8. 4
51 21 14 o
57.7
75.6 19I
- Mo
W
-- Mo
Mo
N.R.
assW
N.R.
99M0
io.2 73.4 92. 5 245
~24 o 5331 5511 18632
12 174 208 421
572t 4607 4937 10228
In the second experiment the carrier V was decreased to 40 /zg in 200 ml of Mo-free nutrient solution containing 9 #Ci 49V and the plants were left for 48 h before sampling. This treatment led to a 3-fold increase in the foliar V to 944 counts/Iooo s per g fresh wt. Table I shows the subsequent purification of nitrate reductase with corresponding radioactivity from these plants compared with effects of equivalent doses of W and Mo given under similar conditions. It is seen that whereas W and Mo accumulate in the fractions rich in nitrate reductase V becomes progressively diluted out. The increase in specific activity of the enzyme during purification was similar for V and W treatments (24 ×) but higher for Mo treatment (35 ×) which has a greater level of enzyme activity due to the inductive effect of Mo. Pre- and posttreatment levels of enzyme activity (nmoles NO 2 produced/I 5 min per g fresh wt) were 164 and 155 for V, 18o and 149 for W, and lO2 and 334 for Mo. In no case did the enzyme activity of the leaves significantly increase as a result of treatment with V. It was therefore clear that no biosynthetically produced V analogue of nitrate reductase was formed under these conditions. This contrasted with W, which induces an enzymically inactive protein 11 and with Mo which is the natural prosthetic metal of the enzyme 13. The atomic radii of the three metals are 1.29, 1.3o and 1.22 for No, W and V, respectively, and the ionic radii of the M4+ state are o.68, o.68 and o.6416 suggesting that the inability of V to form an analogue is related to its size. By analogy, the inability of the W analogue to be enzymically active does not result from altered spatial relationships with the protein but from some other factor, possibly redox potential. Available information 1~ shows W to differ significantly from Mo in several redox systems. The results also suggest that nitrate reductase is less flexible around the Mo site of the protein than nitrogenase. In the latter, a V-containing analogue either shows functional but modified properties or a V-containing protein of similar purification characteristics is produced which influences the activity of diminished amounts of nitrogenase. V shows no affinity with nitrate reductase as it is neither incorporated into, nor seems to modify, residual nitrate reductase protein. lgiochim,
lCiophys. A c l a , 275 (1972) 3 5 5 - 3 5 7
INCORPORATION OF V , W OR M o INTO NITRATE REDUCTASE
357
ACKNOWLEDGEMENTS
We would like to thank Mr C. P. Lloyd-Jones for automated counting facilities, Mr E. F. Watson for growing the plants, and Mr R. J. Fido for technical assistance during this investigation. REFERENCES I J. R. P o s t g a t e , The Chemistry and Biochemistry of Nitrogen Fixation, P l e n u m Press, L o n d o n , I97 I, p. 191 . 2 E. J. H e w i t t a n d D. J. D. Nicholas, in H. F. Linsken, t3. D. Sanwall a n d M. V. Tracey, Modern Methods of Plant Analysis, Vol. 7, Springer, Berlin, 1964, p. 67. 3 J- H. Becking, Plant and Soil, 16 (1962) 171. 4 C. E. M c K e n n a , J. R. B e n e m a n n a n d T. G. Taylor, Biochem. Biophys. Res. Commun., 41 (197 o) I5OI. 5 R. C. B u r n s , W. H. F u c h s m a n a n d R. \V. F. H a r d y , Biochem. Biophys. Res. Commun., 42 (197 I) 353. 6 M. B. Allan, Sci. Mon., 83 (I956) lOO. 7 H. C. J e n s o n a n d R. C. B e t t y , Proc. Linn. Soc. N.S. Wales, 68 (1943) 1. 8 H. T a k a h a s h i a n d A. Nason, Biochim. Biophys. Acta, 23 (1957) 433. 9 R. F. Keeler a n d J. E. Varner, Arch. Biochem. Biophys., 7 ° (1957) 585 • IO Y. M. H e i m e r , J. L. W r a y a n d P. Filner, Plant Physiol., 44 (I969) I197. 1i B. A. N o t t o n a n d E. J. H e w i t t , Biochem. Biophys. Res. Commun., 44 (1971) 7 o2. 12 B. A. N o r t o n a n d E. J. Hewitt, F E B S Lett., I8 (i971) I9. 13 13. A. N o r t o n a n d E. J. H e w i t t , Plant Cell Physiol., i2 (1971) 465. 14 D. B e r t r a n d , Ann. Inst. Pasteur, 68 (I94e) 58. t 5 E. J. H e w i t t , Sand and Water Culture Methods used in the study of Plant Nutrition, C o m m o n w e a l t h B u r e a u of H o r t i c u l t u r e , Tech. C o m m u n . 22, F a r n h a m Royal, E n g l a n d , 2 n d edn, 1966, p. 176. 16 R. B. Heslop a n d P. L. R o b i n s o n , Inorganic Chemistry, Elsevier, A m s t e r d a m , 196o. 17 C. D. H o d g m a n , Handbooh of Chemistry and Physics, T h e Chemical R u b b e r C o m p a n y P u b lishing C o m p a n y , Cleveland, Ohio, 43rd edn, 1961.
Biochim. Biophys. Acta, 275 (1972) 355-357