Enzymatic study on lymphocyte CD38

임파구 CD38의 효소학적 연구

Murine CD38 is a 42 kDa type II glycoprotein expressed on cell surface of both B and T lymphocytes. CD38 is a multifunctional enzyme that catalyzes the formation and hydrolysis of cyclic adenosine diphosphoribose (cADPR): ADP-ribosyl cyclase activity of CD38 catalyzes the formation of cADPR from NAD and cADPR hydrolase activity of CD38 catalyzes the hydrolysis of cADPR to ADP-ribose (ADPR). And also, CD38 has the catalytic activity of NAD glycohydrolase (NADase) which catalyzes the hydrolysis of catalyzes the formation and hydrolysis of cyclic adenosine diphosphoribose (cADPR): ADP-ribosyl cyclase activity of CD38 catalyzes the formation of cADPR from NAD to ADPR. In this study, we attempted to purify CD38 from mouse lymphocytes by using the immobilized anti-CD38 monoclonal antibody. The single step immuno-affinity column chromatography resulted in homogeneous purification, showing a single protein of 42 kDa on a SDS polyacrylamide gel. We have investigated the effects of various inhibitors on the enzyme activities of the purified CD38. Cibacron blue (0.5 mM) inhibited all three enzyme activities of CD38, NADase, ADP-ribosyl cyclase and cADPR hydrolase activities. ADPR (2 mM) showed inhibitory effect on both cADPR hydrolase activity and NADase, but not on ADP-ribosyl cyclase activity. However, ATP (2 mM) inhibited only cADPR hydrolase activity. $Zn^{2+}$ (1 mM) showed similar inhibitory effect as that of ADPR, but activated cyclase activity These results suggest that CD38 has three different catalytic activity domains which might be differentially regulated by their specific inhibitors.