Unusual Enzymatic Hydrolysis of NAD by Solubilized Form of NAD⁺ Glycohydrolase

Abstract

Using solubilized form (sNADase) of membrane-bound porcine brain NAD⁺ glycohydrolase (pNADase), the NADase-catalyzed hydrolysis and transglycosidation reactions of NAD (1) were examined. Unexpectedly, products in the reactions were found to be nicotinamide (5′-O-diphosphono)-β-D-ribofuranoside (4) and adenosine (5). Adenosine 5′-diphosphate (ADP)-ribose (2) and nicotinamide (3) as well as a transglycosylated product, which are formed in a usual NAD/pNADase reaction system, were scarcely produced in the NAD/sNADase system. Setting aside the mechanical aspects of this unusual cleaving, it is quite interesting that the sNADase-catalyzed hydrolytic reaction of NAD resulted in the selective cleavage of the P–O bond of the adenosine side without the appreciable hydrolysis of the labile quaternary nicotinamide-ribose pyridinium linkage.