Abstract
CD38, a bifunctional enzyme capable of both synthesis and hydrolysis of the second messenger cyclic ADP-ribose (cADPR). Using the natural substrate of the enzyme, NAD +, the ratio of ADP-ribosyl cyclase/NAD glycohydrolase of CD38 is about 1/100. Here we describe that human seminal fluid contain a soluble CD38 like enzyme with an apparent M.W. of 49 kDa. When purified this enzyme has a cyclase/NAD glycohydrolase ratio of about 1/120. However, the in situ cyclase/NAD glycohydrolase ratio measured in seminal plasma approaches 1/1. We also found that physiological concentrations of zinc present in the seminal fluid, in the range of 0.6 to 4 mM, are responsible for the modulation of the cyclase/NAD glycohydrolase ratio. This new information indicates that the cyclase/NAD glycohydrolase ratio can be modified in vivo.
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