Glutamate 94 of [2Fe-2S]-ferredoxins is important for efficient electron transfer in the 1:1 complex formed with ferredoxin-glutamate synthase (GltS) from Synechocystis sp. PCC 6803.
We have analyzed the role of critical amino acid residues involved in the interaction between ferredoxin and ferredoxin-glutamate synthase (GOGAT) encoded by the gltS gene from the cyanobacterium Synechocystis sp. PCC 6803. Our results indicated that the glutamate 94 residue of Anabaena 7120 ferredoxin (= E92 of the Synechocystis 6803 ferredoxin) was necessary for an efficient electron transfer to GOGAT comparable to ferredoxin:NADP-reductase, nitrite reductase and nitrate reductase [Schmitz and Böhme (1995) Biochim. Biophys. Acta 1231, 335-341]. The K(m) value determined for wt-ferredoxins and mutant E94Q (and E92Q) was 1 muM, respectively, and activity loss of E94Q was due to a lowered Vmax. Exchange of residue F65 for aliphatic substitutions, which was crucial to electron transfer to ferredoxin:NADP-reductase and nitrite reductase, exhibited only small effects on glutamate synthase-dependent activity while heterocyst ferredoxin and flavodoxin were almost inactive as electron donors. In contrast to data reported for the spinach system, the stoichiometry of the cross-linked complex between ferredoxin and glutamate synthase was 1:1.
Schmitz
S
S
Botanisches Institut der Universität Bonn, Abteilung für Molekulare Biochemie, Germany.
Navarro
F
F
Kutzki
C K
CK
Florencio
F J
FJ
Böhme
H
H
D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport; D005288:Ferredoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D007700:Kinetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D005288:Ferredoxins; D011994:Recombinant Proteins; D018698:Glutamic Acid; D000594:Amino Acid Oxidoreductases; C042233:glutamate synthase (ferredoxin)