Pyridine nucleotidenitrate reductase from Hansenula anomala a nitrate reducing yeast.

The recent elucidation of the enzyme systems involved in nitrate reduction in Neurospora crassa (Evans and Nason, 1952; Nason and Evans, 1953); Bacillus pumilis (Taniguchi et al., 1953); Escherichia coli (Taniguchi et al., 1956; Nicholas and Nason, 1955) and higher plants (Evans and Nason, 1953), has renewed interest in the general problem of nitrate reduction and nitrate assimilation in microorganisms. The demonstration that diverse pathways of reduction may exist and, indeed, may coexist in certain organisms (Cheng et al., 1955; Taniguchi et al., 1956) indicates that a further systematic attack is needed before any over-all generalizations can be made. Since no previous reports of the cell-free enzyme system from yeast have appeared in the literature, a study of the nitrate reducing system of the nitrate reducing yeast, Hansenula anomala, was undertaken. The observations reported in this paper demonstrate that yeast nitrate reductase is a metalloflavoprotein requiring reduced pyridine nucleotide as a hydrogen donor. A preliminary report of this work has appeared (Silver and Nickerson, 1956).