Pathways of NADP+ and NAD+ degradation by Aspergillus niger extracts

Extracts of an Aspergillus niger strain catalyzed degradation of NADP(+) and NAD(+) optimally at pH 4 and at pH 8 via a non-previously recognized pathway. Through this pathway NADP(+) was dephosphorylated to NAD(+) which then was cleaved to nicotinamide riboside plus ADP. The ADP formed was furtherly hydrolyzed to adenosine via the intermediate formation of AMP. At pH 4, the N-glycosidic linkage of adenosine was hydrolytically cleaved leading to the formation of adenine plus ribose. The extracts also catalyzed dephosphorylation of nicotinamide mononucleotide yielding nicotinamide riboside which could not be furtherly degraded. Phosphate release from each of NADP(+), NAD(+), ADP, and AMP was similarly affected as phosphate release from phenyl phosphate when tested under different experimental conditions. These conditions included different pH values, different temperatures, exposing the extracts to dialysis or to 75 degrees C for 5 min and addition of molybdate or magnesium to the reaction mixtures. NADP(+) and NAD(+) dephosphorylating enzymes were characterized as acid and alkaline phosphatases. Separation of the acid phosphatase from the alkaline phosphatase was achieved using Sephadex G-100 column chromatography.