Hirasawa M, Nakayama M, Kim SK, Hase T, Knaff DB. Chemical modification studies of tryptophan, arginine and lysine residues in maize chloroplast ferredoxin:sulfite oxidoreductase.
Photosynth Res 2005;
86:325-36. [PMID:
16307304 DOI:
10.1007/s11120-005-6966-y]
[Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Accepted: 05/04/2005] [Indexed: 05/05/2023]
Abstract
The ferredoxin-dependent sulfite reductase from maize was treated, in separate experiments, with three different covalent modifiers of specific amino acid side chains. Treatment with the tryptophan-modifying reagent, N-bromosuccinimide (NBS), resulted in a loss of enzymatic activity with both the physiological donor for the enzyme, reduced ferredoxin, and with reduced methyl viologen, a non-physiological electron donor. Formation of the 1:1 ferredoxin/sulfite reductase complex prior to treating the enzyme with NBS completely protected the enzyme against the loss of both activities. Neither the secondary structure, nor the oxidation-reduction midpoint potential (Em) values of the siroheme and [4Fe-4S] cluster prosthetic groups of sulfite reductase, nor the binding affinity of the enzyme for ferredoxin were affected by NBS treatment. Treatment of sulfite reductase with the lysine-modifying reagent, N-acetylsuccinimide, inhibited the ferredoxin-linked activity of the enzyme without inhibiting the methyl viologen-linked activity. Complex formation with ferredoxin protects the enzyme against the inhibition of ferredoxin-linked activity produced by treatment with N-acetylsuccinimide. Treatment of sulfite reductase with N-acetylsuccinimide also decreased the binding affinity of the enzyme for ferredoxin. Treatment of sulfite reductase with the arginine-modifying reagent, phenylglyoxal, inhibited both the ferredoxin-linked and methyl viologen-linked activities of the enzyme but had a significantly greater effect on the ferredoxin-dependent activity than on the reduced methyl viologen-linked activity. The effects of these three inhibitory treatments are consistent with a possible role for a tryptophan residue the catalytic mechanism of sulfite reductase and for lysine and arginine residues at the ferredoxin-binding site of the enzyme.
Collapse