A. Yamashita et al., ACYL-COA-BINDING AND ACYLATION OF UDP-GLUCURONOSYLTRANSFERASE ISOFORMS OF RAT-LIVER - THEIR EFFECT ON ENZYME-ACTIVITY, Biochemical journal, 312, 1995, pp. 301-308
When [C-14]arachidonoyl-CoA was incubated with crude extracts of rat l
iver microsomes, [C-14]arachidonic acid was incorporated into many pro
teins, suggesting that modification of these proteins with fatty acid,
i.e. acylation, occurred. Using [C-14]arachidonoyl-CoA labelling assa
y, 50 and 53 kDa proteins were purified from rat liver microsomes to n
ear homogeneity by sequential chromatography on Red-Toyopearl, hydroxy
apatite, heparin-Toyopearl, Blue-Toyopearl and UDP-hexanolamineagarose
. Acylation of the 50 and 53 kDa proteins occurred in the absence of a
ny other protein, suggesting that these molecules catalyse autoacylati
on. The acylation was dependent on the length of the incubation period
and the concentration of [C-14]arachidonoyl-CoA. The 50 and 53 kDa pr
oteins also had acyl-CoA-binding activity; initial rates of acyl-CoA b
inding and acylation were 0.25 and 0.004 min(-1) respectively. The pro
teins also had weak but distinct acyl-CoA-hydrolysing activity (0.006
min(-1)). These results suggest that the proteins catalysed the sequen
tial reactions of binding to acyl-CoA, autoacylation, and hydrolysis o
f fatty acid. N-terminal amino acid sequencing analysis showed these p
roteins to be UDP-glucuronosyltransferase (UDPGT) isoforms. UDPGT acti
vity was inhibited by arachidonoyl-CoA. These results suggest that bin
ding of acyl-CoA and acylation of UDPGT isoforms regulate the enzyme a
ctivities, implying a possible novel function for fatty acyl-CoA in gl
ucuronidation, which is involved in the metabolism of drugs, steroids
and bilirubin.