Purification and Characterization of ADP-Ribosyl Cyclase from Euglena gracilis

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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 K_m value for NAD⁺ was estimated to be 0.4mM, 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.