Berthelier V, Tixier J M, Muller-Steffner H, Schuber F, Deterre P
Laboratoire d'Immunologie Cellulaire, Unité Associée 625 du Centre National de la Recherche Scientifique, Groupe Hospitalier Pitié-Salpêtière, 83 boulevard de l'Hôpital, 75013 Paris, France.
Biochem J. 1998 Mar 15;330 ( Pt 3)(Pt 3):1383-90. doi: 10.1042/bj3301383.
The leucoyte surface antigen CD38 has been shown to be an ecto-enzyme with multiple catalytic activities. It is principally a NAD+ glycohydrolase that transforms NAD+ into ADP-ribose and nicotinamide. CD38 is also able to produce small amounts of cyclic ADP-ribose (ADP-ribosyl cyclase activity) and to hydrolyse this cyclic metabolite into ADP-ribose (cyclic ADP-ribose hydrolase activity). To classify CD38 among the enzymes that transfer the ADP-ribosyl moiety of NAD+ to a variety of acceptors, we have investigated its substrate specificity and some characteristics of its kinetic and molecular mechanisms. We find that CD38-catalysed cleavage of the nicotinamide-ribose bond results in the formation of an E.ADP-ribosyl intermediary complex, which is common to all reaction pathways; this intermediate reacts (1) with acceptors such as water (hydrolysis), methanol (methanolysis) or pyridine (transglycosidation), and (2) intramolecularly, yielding cyclic ADP-ribose with a low efficiency. This reaction scheme is also followed when using nicotinamide guanine dinucleotide as an alternative substrate; in this case, however, the cyclization process is highly favoured. The results obtained here are not compatible with the prevailing model for the mode of action of CD38, according to which this enzyme produces first cyclic ADP-ribose which is then immediately hydrolysed into ADP-ribose (i.e. sequential ADP-ribosyl cyclase and cyclic ADP-ribose hydrolase activities). We show instead that the cyclic metabolite was a reaction product of CD38 rather than an obligatory reaction intermediate during the glycohydrolase activity. Altogether our results lead to the conclusion that CD38 is an authentic 'classical' NAD(P)+ glycohydrolase (EC 3.2.2.6).
白细胞表面抗原CD38已被证明是一种具有多种催化活性的胞外酶。它主要是一种NAD + 糖水解酶，可将NAD + 转化为ADP-核糖和烟酰胺。CD38还能够产生少量的环ADP-核糖（ADP-核糖基环化酶活性），并将这种环状代谢物水解为ADP-核糖（环ADP-核糖水解酶活性）。为了将CD38归类于将NAD + 的ADP-核糖基部分转移到各种受体的酶中，我们研究了其底物特异性以及动力学和分子机制的一些特征。我们发现，CD38催化的烟酰胺-核糖键的裂解导致形成E.ADP-核糖中间体复合物，这是所有反应途径共有的；该中间体与诸如水（水解）、甲醇（甲醇解）或吡啶（转糖苷作用）等受体反应，以及（2）分子内反应，低效地产生环ADP-核糖。当使用烟酰胺鸟嘌呤二核苷酸作为替代底物时，也遵循该反应方案；然而，在这种情况下，环化过程非常有利。这里获得的结果与CD38作用模式的主流模型不相符，根据该模型，这种酶首先产生环ADP-核糖，然后立即水解为ADP-核糖（即顺序的ADP-核糖基环化酶和环ADP-核糖水解酶活性）。相反，我们表明环状代谢物是CD38的反应产物，而不是糖水解酶活性期间的必需反应中间体。总之，我们的结果得出结论，CD38是一种真正的“经典”NAD(P)+ 糖水解酶（EC 3.2.2.6）。
