Abstract
crassa, demonstrated that the inactive apoprotein of nitrate reductase in extracts of the mutant could be reconstituted by the addition of denatured preparations of purified molybdoenzymes from animal, fungal, or bacterial origin. This crucial finding showed that mol- ybdoenzymes contain a dissociable entity fitting the description of a cofactor and provided further evidence for the universality of the molybdenum cofactor. The
Highlights
All molybdenum-containing enzymes other than nitrogenase catalyze either oxidative hydroxylations or reductive dehydroxylations [1, 2]
In a series of subsequent studies Nason and co-workers [8,9,10,11], using the pleiotropic nit-1 mutant of Neurospora crassa, demonstrated that theinactive apoprotein of nitrate reductase in extracts of the mutant could be reconstituted by the addition of denatured preparationsof purified molybdoenzymesfrom animal, fungal, or bacterial origin
This crucial finding showed that molybdoenzymes contain a dissociable entity fitting the description of a cofactor and provided further evidence for the universality of the molybdenum cofactor
Summary
Unlike most of the known cofactors, the molybdenum cofactor is not amenable to normal procedures used in the isolation of natural products. In our laboratory the elucidation of the structure shown in Fig. 1for the cofactor required the use of purified molybdoenzymes as starting materials and was the culmination of structural studies on several inactive derivatives of the active cofactor The earliest of these derivatives to be characterized, Form A, is formed when proteins or wholecell extracts containing the cofactor are subjected to vigorous oxidation at 100 "C in the presence of 12/KI[15].The bright fluorescenceof Form A permits detection and identification of the compound during the purification procedure. The possible existence of a variant form of molybdenum cofactor was initially proposed byKriiger and Meyer [22, 23] who reported that CO dehydrogenase from Pseudomonas carboxydoflava yielded an inactive pterin larger than the corresponding derivative from milk xanthine oxidase.
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