IN-VITRO SYNTHESIS OF THE IRON-MOLYBDENUM COFACTOR AND MATURATION OF THE NIF-ENCODED APODINITROGENASE - EFFECT OF SUBSTITUTION OF VNFH FOR NIFH

NIFH (the nifH gene product) has several functions in the nitrogenase enzyme system. In addition to reducing dinitrogenase during nitrogenas e turnover, NIFH functions in the biosynthesis of the iron-molybdenum cofactor (FeMo-co), and in the processing of alpha(2) beta(2) apodinit rogenase 1 (a catalytically inactive form of dinitrogenase 1 that lack s the FeMo-co) to the FeMo-co-activatable alpha(2) beta(2) gamma(2) fo rm, The molybdenum-independent nitrogenase 2 (unf-encoded) has a disti nct dinitrogenase reductase protein, VNFH, We investigated the ability of VNFH to function in the in vitro biosynthesis of FeMo-co and in th e maturation of apodinitrogenase 1. VNFH can replace NIFH in both the biosynthesis of FeMo-co and in the maturation of apodinitrogenase 1. T hese results suggest that the dinitrogenase reductase proteins do not specify the heterometal incorporated into the cofactors of the respect ive nitrogenase enzymes, The specificity for the incorporation of moly bdenum into FeMo-co was also examined using the in vitro FeMo-co synth esis assay system.