AJP - Cell Physiology, Vol 245, Issue 5 449-C456, Copyright © 1983 by American Physiological Society
NAD+-dependent ADP-ribosyltransferase in renal brush-border membranes
S. A. Kempson and N. P. Curthoys
Oxidized nicotinamide adenine dinucleotide (NAD+) in cytosol may interact
with renal brush-border membranes (BBM) and inhibit BBM phosphate
transport. The possible mechanism of interaction was investigated in the
present study. Incubation of BBM with [adenine-3H]NAD+ led to acid-stable
binding of 3H to the BBM, in contrast there was no binding of 14C when
[carbonyl-14C]NAD+ was used. The data are consistent with an
ADP-ribosylation mechanism involving transfer of ADP-ribose from NAD+ to
BBM. This was confirmed by using [adenylate-32P]NAD+ and by the release of
bound 32P in the form of 5'-[32P]AMP when the BBM were treated with snake
venom phosphodiesterase. After gradient centrifugation of BBM the
ADP-ribosyltransferase was recovered at the same density as known BBM
enzymes, indicating that ADP-ribosyltransferase is an intrinsic BBM
component and not a contaminant. These findings indicate that cytosolic
NAD+ may be used for ADP-ribosylation of BBM proteins and that this may be
a mechanism for regulating the BBM phosphate transport system.
