Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Reduced ferredoxin can serve as electron donor in the 6-electron reduction of nitrite to ammonia catalyzed by spinach nitrite reductase. We have examined interactions between nitrite reductase and its substrates, ferredoxin and nitrite, with emphasis upon protein-protein interactions between ferredoxin and nitrite reductase. Ferredoxin, of the proteins tested, is the most effective in retarding low ionic strength inactivation of nitrite reductase. The interaction appears to be electrostatic, and the apparent Kd, calculated from the concentration dependence of ferredoxin protection, is about 1 microM in 2 mM Tris. Chemical modification of carboxyl residues of ferredoxin resulting in a change of charge reduces its reactivity with both ferredoxin:NADP+ oxidoreductase and nitrite reductase, indicating the importance of charge-charge interactions. Cross-linking studies provided no evidence for a ternary complex containing the oxidoreductase and nitrite reductase but indicated that the two enzymes will compete for ferredoxin, possibly using the same site (or overlapping sites) on the ferredoxin. A complex containing ferredoxin:NADP+ oxidoreductase, ferredoxin, and cytochrome c was detected, indicating that ferredoxin has different binding sites for cytochrome c and ferredoxin:NADP+ oxidoreductase. Active cross-linked complexes of ferredoxin and nitrite reductase were obtained and were less sensitive to low ionic strength inactivation than free reductase and had decreased ferredoxin-supported nitrite reductase activity. The evidence presented of protein-protein interactions between ferredoxin and nitrite reductase indicates that ferredoxin is indeed the specific physiological electron donor to the reductase.
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PMID:Interactions between spinach ferredoxin-nitrite reductase and its substrates. Evidence for the specificity of ferredoxin. 299 5

The in situ localization of the chloroplast enzymes ribulose-1,5-bisphosphate carboxylase (Rubisco), Rubisco activase, ribose-5-phosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, aldolase, nitrite reductase, ferredoxin-NADP+ reductase, and H+-ATP synthase was studied by immunoelectron microscopy in Chlamydomonas reinhardtii. Immunogold labeling revealed that, despite Rubisco in the pyrenoid matrix, Calvin cycle enzymes, Rubisco activase, nitrite reductase, ferredoxin-NADP+ reductase, and H+-ATP synthase are associated predominantly with chloroplast thylakoid membranes and the inner surface of the pyrenoid membrane. This is in accord with previous enzyme localization studies in higher plants (K.H. Suss, C. Arkona, R. Manteuffel, K. Adler [1993] Proc Natl Acad Sci USA 90: 5514-5518). Pyrenoid tubules do not contain these enzymes. The pyrenoid matrix consists of Rubisco but is devoid of the other photosynthetic enzymes investigated. Evidence for the occurrence of two Rubisco forms differing in their spatial localization has also been obtained: Rubisco form I appears to be membrane associated like other Calvin cycle components, whereas Rubisco form II is confined to the pyrenoid matrix. It is proposed that enzyme form I represents an active Rubisco when assembled into Calvin cycle enzyme complexes, whereas Rubisco form II may be part of a CO2-concentrating mechanism. Pyrenoidal Calvin cycle complexes are thought to be highly active in CO2 fixation and important for the synthesis of starch around the pyrenoid.
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PMID:In Situ Association of Calvin Cycle Enzymes, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activase, Ferredoxin-NADP+ Reductase, and Nitrite Reductase with Thylakoid and Pyrenoid Membranes of Chlamydomonas reinhardtii Chloroplasts as Revealed by Immunoelectron Microscopy. 1222 43