Purification and Characterization of ADP-Ribosyl Cyclase from Euglena gracilis

ADP-ribosyl cyclase, which catalyzes the conversion from NAD+ to cyclic adenosine diphosphoribose (cADPR), is proposed to participate in cell cycle regulation in Euglena gracilis. This enzyme, which was found as a membrane-bound protein, was purified almost the homogeneity after solubilization with deoxycholate, and found to be a monomeric protein with a molecular mass of 40 kDa. Its Km value for NAD+ was estimated to be 0.4 mM, and cADPR, a product of the enzyme, inhibited the enzyme competitively with respect to NAD+ whereas another product, nicotinamide, showed noncompetitive (mixed-type) inhibition. In contrast to mammalian CD38 and BST-1, Euglena ADP-ribosyl cyclase lacked cADPR hydrolase activity. Key words: ADP-ribosyl cyclase, CD38, cell cycle regulation, cyclic ADP-ribose, Euglena gracilis. ADP-ribosyl cyclase, which catalyzes the synthesis of cADPR from NAD+ with the concomitant formation of nicotinamide, has been purified from Aplysia ovotestis (1). In mammalian cells, the synthesis of cADPR from NAD+ i