AJP - Renal Physiology, Vol 249, Issue 3 366-F373, Copyright © 1985 by American Physiological Society
NAD-glycohydrolase in renal brush border membranes
S. A. Kempson
NAD is hydrolyzed during incubation with isolated renal brush border
membranes (BBM). The specific enzymatic mechanisms have not been identified
apart from the activity of ADP-ribosyltransferase, which accounts for a
very small proportion of the total hydrolysis. In the present study, an
NAD-glycohydrolase (NGH) was identified in the renal BBM using the
cyanide-addition assay to monitor hydrolysis of NAD at the
nicotinamide-ribose bond. The production of nicotinamide and ADP-ribose,
the expected reaction products, was determined by thin-layer
chromatography. The NGH was enriched ninefold in the BBM fraction and
accounted for 36% of the total rate of NAD hydrolysis by BBM enzymes at pH
7.4. Assay of NGH in sealed BBM vesicles subjected to osmotic shock
indicated that about 23% of the NGH is exposed on the cytoplasmic surface
of the BBM. The enzyme was inhibited by nicotinamide in vitro and also when
the nicotinamide was administered in vivo, suggesting, indirectly, that the
enzyme may play a role in mediating the effects of nicotinamide on BBM
phosphate transport.
