Ionic interactions in the nitrogenase complex. Properties of Fe-protein containing substitutions for Arg-100.

摘要: A series of Azotobacter vinelandii strains have been constructed in which the nitrogenase Fe-protein (Av2) was altered by substitutions for Arg-100. This invariant residue is a likely partner salt bridge with MoFe-protein and, some species, site reversible regulation ADP-ribosylation (Pope, M. R., Murrell, S. A., and Ludden, P. W. (1985) Proc. Natl. Acad. Sci. U. A. 82, 3173-3177). Although we find that arginine optimum amino acid, other residues this position could support diazotrophic growth. These results were surprising because Klebsiella pneumoniae substituted His-100 had reported to be inactive (Lowery, R. G., Chang, C. L., Davis, L. C., McKenna, M.-C., Stevens, J., (1989) Biochemistry 28, 1206-1212). Two Fe-proteins (Av2-R100Y, tyrosyl form, Av2-R100H, histidyl form) isolated contrast earlier report, found both activity acetylene reduction. However, proteins exhibited decreased maximum velocity (35 3% wild type, respectively) strongly inhibited excess MoFe-protein. adverse parameters also manifest increased sensitivity inhibition salts. Indeed, Av2-R100H so significant its masked normal assay easily missed. In addition, substrate reduction substantially uncoupled from MgATP hydrolysis. suggest Arg-100 may decrease affinity prior electron transfer but increase after transfer. Hence, role provide balance stabilities these two complexes efficiency