ENZYME PROPERTIES OF APLYSIA ADP-RIBOSYL CYCLASE - COMPARISON WITH NAD GLYCOHYDROLASE OF CD38 ANTIGEN

An ecto-enzyme of NAD glycohydrolase (NADase) induced by retinoic acid in HL-60 cells is attributed to the molecule of CD38 antigen [Kontani, K., Nishina, H., Ohoka, Y., Takahashi, K., and Katada, T. (1993) J. Biol. Chem. 268, 16895-16898]. CD38 antigen has an amino acid sequence homologous to Aplysia ADP-ribosyl cyclase which generates cyclic adenosine diphosphoribose (cADPR) and nicotinamide (NA) from beta-NAD(+). On the basis of this sequence homology, we compared enzyme properties between CD38 NADase expressed as a fusion protein in Escherichia coli and ADP-ribosyl cyclase purified from the ovotestis of Aplysia kurodai. 1) beta-NAD(+) analogs, nicotinamide 1, N-6-ethenoadenine dinucleotide, and nicotinamide hypoxanthine dinucleotide, did not serve as good substrates for the ADP-ribosyl cyclase, suggesting that the intact adenine ring of beta-NAD(+) was required for the cyclase-catalyzed reaction. On the other hand, CD38 NADase utilized the NAD analogs to form ADP-ribose and NA. 2) Kinetic analyses of the ADP-ribosyl cyclase reaction revealed that NA was first released from the substrate (beta-NAD(+))-enzyme complex, followed by the release of another product, cADPR, which was capable of interacting with the free enzyme. 3) The enzyme reaction catalyzed by the ADP-ribosyl cyclase was fully reversible; beta-NAD(+) could be formed from cADPR and NA with a velocity similar to that observed in the degradation of beta-NAD(+). However, CD38 NADase did not catalyze the reverse reaction to form beta-NAD(+) from ADP-ribose and NA. 4) The CD38 NADase activity was, but the ADP-ribosyl cyclase activity was not, inhibited by dithiothreitol. These results indicated that enzyme reactions catalyzed by Aplysia ADP-ribosyl cyclase and CD38 NADase were quite different from each other in terms of their substrate specificities, reversible reactions, and susceptibilities to dithiothreitol, though both enzymes cleaved the N-glycoside bond of beta-NAD(+) resulting in the liberation of NA.