The properties of nucleotide complexes with microsomal cytochrome reductase.

Under anaerobic conditions the addition of reduced diphosphopyridine nucleotide to stoichiometric amounts of microsomal cytochrome reductase yields reduced flavin and a nucleotideenzyme complex characterized by a 315-rnp absorption peak (2). The properties of the reactive sulfhydryl groups of the enzyme and the evidence for the participation of only one such group in this reaction have been described (3). In the present study the nature of the interaction of nucleotides with microsomal cytochrome reductase was examined in more detail. Direct evidence for nucleotide binding to the enzyme was obtained. Reduced triphosphopyridine nucleotide, analogues of reduced diphosphopyridine nucleotide and other nucleotides were then used to demonstrate the participation of various parts of the substrate molecule in interactions with microsomal cytochrome reductase and to implicate protein groups in addition to the essential sulfhydryl group in nucleotide binding.