A. Yamashita et al., INHIBITION OF UDP-GLUCURONOSYLTRANSFERASE ACTIVITY BY FATTY ACYL-COA - KINETIC-STUDIES AND STRUCTURE-ACTIVITY RELATIONSHIP, Biochemical pharmacology, 53(4), 1997, pp. 561-570
We previously identified and purified UDP-glucuronosyltransferase (UGT
) isoforms as targets of protein acylation from rat liver microsomes (
Yamashita et al., Biochem J 312: 301-308, 1995). The acylation of UGT
isoforms occurred upon incubation with acyl-CoA without another protei
n acyltransferase, suggesting that it was autoacylation. The study rev
ealed the interaction of UGT isoforms with acyl-CoA. In the present st
udy, the effects of fatty acyl-CoA on UGT activities were examined tho
roughly, using a rat liver microsomal and purified enzyme fractions. T
he UGT activities of both fractions were inhibited by acyl-CoA in a co
ncentration-dependent manner. The effect of acyl-CoA was observed on t
he activities toward various substrates, suggesting that the effect sh
ows the wide spectrum of the isoforms of UGT. To assess the mechanism
underlying the inhibition of UGT activity by acyl-CoA, the relationshi
p of the inhibition, acyl-CoA binding to the proteins, and changes in
the tertiary structure of the enzyme were examined. The kinetics of th
ese phenomena were related closely with each other. Furthermore, the i
nhibition of UGT activity was specified for acyl-CoA, though a structu
rally related compound, acyl-3'-dephosphoCoA, had no inhibitory effect
. The results suggested that the specific binding of acyl-CoA to UGT i
soforms induced conformational changes of the enzymes and resultant in
hibition of UGT activity. (C) 1997 Elsevier Science Inc.