Adenosine diphosphate ribose pyrophosphohydrolase in human skin.

Abstract

Adenosine diphosphate ribose (ADPR) pyrophosphohydrolase (ADPR-PPase), which catalyzes the hydrolysis of ADPR to yield adenosine monophosphate (AMP) and ribose-5'-phosphate, was assayed in human penile foreskin. Since ADPR is formed from nicotinamide adenine dinucleotide (NAD) by NAD glycohydrolase (NADase), NADase was also assayed in human skin. The skin tissue obtained by circumcision was separated into three layers; epidermis of the outer prepuce, epidermis of the inner prepuce, and dermis. ADPR-PPase was found to be present in all of the three layers with nearly equal activity. NADase was also present in the epidermis of both the outer and inner prepuce, being about two times higher in the latter, but no activity was found in the dermis. When expressed in units of the same specific activity; i.e., micromoles product formed per hour per mg protein, the ADPR-PPase of human skin had two to five times greater activity than did NADase. The ADPR-PPase of human skin was activated by Mg(+2), but inhibited by AMP and ATP. These results suggest that the breakdown of NAD occurs in human skin via ADPR to AMP and ribose-5'-phosphate by sequential action of NADase and ADPR-PPase.