Effect of hypophysectomy on liver diphosphopyridine nucleotide: the role of nicotinamide

Abstract

The effectiveness of nicotinamide and 5′-methyl nicotinamide as inhibitors of nuclear NAD nucleosidase and poly ADP-ribose polymerase from rat liver has been investigated. Nicotinamide inhibited the NAD nucleosidase and the poly ADP-ribose polymerase with Ki's of 5 · 10−4 M and 2 · 10−5 M, respectively, 5′-methyl nicotinamide with Ki's of 3.3 · 10−4 M and 2 · 10−4 M, respectively. As both nicotinamide and 5′-methyl nicotinamide are similarly effective inhibitors of these enzymes, inhibition at these sites cannot explain the different effects that nicotinamide and 5-methyl nicotinamide have on hepatic NAD synthesis (Clark and Pinder, 1969). It is suggested therefore that the poly ADP-ribose polymerase is more likely involved in the control of DNA synthesis than in NAD synthesis (as suggested elsewhere).