US EPA

6095932 

Journal Article 

PROSTHETIC COMPONENTS AND ESSENTIAL GROUPS FOR ACTIVITY IN FERREDOXIN NITRITE REDUCTASE FROM CHLAMYDOMONAS-REINHARDTII 

Saab, AN; Sloan, KB 

1989 

57 

2 

259-270 

10.1016/0304-5102(89)80235-4 

WOS:A1989CG17700012 

http://www.sciencedirect.com/science/article/pii/0304510289802354
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Ferredoxin-nitrite reductase (ammonium ferredoxin oxidoreductase, EC 1.7.7.1) from the green alga Chlamydomonas reinhardtii, M.W. = 86 000, has per molecule 5 iron atoms (of which one is in siroheme) and 4 labile sulfides, forming one 4Fe-4S cluster. Redox titration of the enzyme shows a midpoint potential for the siroheme of −160 mV, at pH 7.5. The enzyme molecule is composed by 884 amino acids, which gives an isoelectric point of 6.2. Colorimetric titration with 5,5'-Dithiobis(2-nitrobenzoic) acid of native ferredoxin-nitrite reductase, in the presence of urea, with or without boron hydride, showed the presence of 11 -SH groups from cysteine and 2 sulfur bridges. A maximum of 5 -SH groups are essentially required for catalytic activity, deduced from the enzyme previously modified with p-hydroxy-mercury benzoate, methyl methane thiosulphonate, N-ethyl maleimide and iodoacetamide. On the other hand, ferredoxin-nitrite reductase is completely inhibited by treatment with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, indicating the necessity of carboxyl groups for the activity. This treatment produces a significant alteration in the visible absorption spectrum of the enzyme.