19] Formation of nicotinamide ribose diphosphate ribose, a new metabolite of the NAD pathway, by Aspergillus niger

Abstract

Publisher Summary This chapter discusses the formation of nicotinamide ribose diphosphate ribose (NAmRDPR) by Aspergillus niger. nicotinamide adenine dinucleotide (NAD) contains two β-riboside linkages potentially susceptible to hydrolytic cleavage. Generally, NAD is degraded at the nicotinamide-ribose linkage by NAD glycohydrolases that are widely distributed in microorganisms. However, Aspergillus niger characteristically possesses another route for NAD degradation. The enzyme preparation of this fungus splits NAD at the adenine-ribose linkage to form NAmRDPR and adenine. A purine nucleosidase-type enzyme has been shown to be involved in the degradation of NAD. This new metabolite, NAmRDPR, is also formed, from either nicotinic acid or nicotinamide, as a final metabolite of the Preiss-Handler pathway of NAD synthesis, in growing mycelium of the organism. For the preparation of NAmRDPR, NAD is incubated with the enzyme preparation of A. niger at pH 4.0. The NAmRDPR formed is isolated from the reaction mixture, using a Dowex 1 X2 formate column. The assay procedure for the purification of the NAD-degrading nucleosidase is discussed in detail in this chapter. Formation of the NAmRDPR by growing mycelia of Aspergillus niger is also discussed in the chapter.