Evidence for NAD Nucleosidase in Rabbit-Liver Lysosomes

Abstract

A method is described for the isolation of secondary lysosomes from homogenates of rabbit liver. The uptake of Triton WR-1339 by rabbit-liver lysosomes when administered by intraperitoneal injection was used to decrease the density of secondary lysosomes. Lysosomal fractions prepared by this method contain an NAD nucleosidase (NAD glycohydrolase, EC 3.2.2.5), an enzyme which has previously been considered to be associated with other subcellular fractions. The enzyme has maximum activity at pH 6 and cleaves both NAD and NADP. It is inhibited by nicotinamide (Ki = 4.5 mM) and by HgCl2. Both nucleosidase and 2′-nucleotidase show in-vitro latency typical of lysosomal acid hydrolases. Rabbit-liver plasma-membrane fractions were isolated which contained most 5′-nucleotidase but relatively little nucleosidase, whereas rabbit liver lysosomes contain both 5′-nucleotidase and nucleosidase enzymes but little adenyl cyclase.