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Further Characterization of Nitrate and Nitrite Reductases from Chlamydomonas reinhardii
Author(s) -
BAREA J. L.,
MALDONADO J. M.,
CÁRDENAS J.
Publication year - 1976
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1976.tb02251.x
Subject(s) - nitrate reductase , nitrate , nitrite , chlamydomonas , nitrite reductase , chemistry , nitrogen assimilation , biochemistry , molybdenum cofactor , diaphorase , nad+ kinase , reductase , ferredoxin , enzyme , organic chemistry , mutant , gene
The enzymes responsible for nitrate reduction in Chlamydomonas reinhardii , namely NADH‐nitrate reductase and ferredoxin‐nitrite reductase, have been further characterized. The first activity of the nitrate reducing complex, NADH‐diaphorase, is protected by FAD against thermic inactivation. This fact suggests an important structural and functional role for this nucleotide in the first moiety of the nitrate reductase complex. The effect of p ‐hydroxymercuribenzoate on the diaphorase activity and the protection by NADH against its inactivation indicate that some—SH groups participate in the electron transfer mediated by diaphorase. Radioactive labelling of nitrate reductase with 99 Mo and 185 W as well as competition experiments between Mo and W indicate that molybdenum is an essential component of terminal nitrate reductase activity. Iron seems to participate in the redox processes mediated by both nitrate and nitrite reductases as suggested by experiments performed at physiological level. Finally a tentative mechanism for the whole process of nitrate assimilation in Chlamydomonas is proposed.