Inhibition kinetics of hepatic microsomal long chain fatty acid-CoA ligase by 2-arylpropionic acid non-steroidal anti-inflammatory drugs.
Microsomal long chain fatty acid CoA ligase (EC 6.2.1.3) has been implicated in the formation of CoA thioesters of xenobiotics containing a carboxylic acid moiety. In this study we have demonstrated that the microsomal enzyme from rat liver exhibits biphasic kinetics for the formation of palmitoyl-CoA, i.e. there are high affinity low capacity Kmhigh, 1.6 microM, Vmaxhigh, 12.9 nmol/mg/min) and low affinity high capacity (Kmlow, 506 microM, Vmaxlow, 58.3 nmol/mg/min) components. Inhibition of the high affinity isoform was studied using the R and S enantiomers of ibuprofen, fenoprofen, ketoprofen and naproxen. The high affinity component of palmitoyl-CoA formation was competitively inhibited by R-fenoprofen (Ki 15.4 microM) while R-ibuprofen exhibited mixed inhibition kinetics. In contrast the R and S enantiomers of ketoprofen and naproxen were non-competitive inhibitors. This diversity of inhibition kinetics observed argues in favour of a binding site in addition to the catalytic site. A competitive interaction with the high affinity form correlated with literature evidence of enantiospecific chiral inversion and "hybrid" triglyceride formation for the R enantiomers of fenoprofen and ibuprofen. Paradoxically, R-ketoprofen which is extensively inverted in rats was a non-competitive inhibitor of palmitoyl-CoA formation by the high affinity isoform suggesting that it may not act as an alternate substrate. The results of this study clearly indicate that formation of R-2-arylpropionate-CoAs is not fully explained by interaction with the high affinity isoform of a microsomal long chain (palmitoyl) CoA ligase and therefore the involvement of other isoforms cannot be discounted.
Knights
K M
KM
Dept of Clinical Pharmacology, Flinders University of South Australia.
Jones
M E
ME
D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D001667:Binding, Competitive; D003066:Coenzyme A Ligases / Q000037:antagonists & inhibitors*; D005279:Fenoprofen / Q000494:pharmacology; D007052:Ibuprofen / Q000494:pharmacology; D007660:Ketoprofen / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009288:Naproxen / Q000494:pharmacology; D010171:Palmitoyl Coenzyme A / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013237:Stereoisomerism; D013379:Substrate Specificity; D014280:Triglycerides / Q000096:biosynthesis; D000098859:Long-Chain-Fatty-Acid-CoA Ligase
D000894:Anti-Inflammatory Agents, Non-Steroidal; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014280:Triglycerides; D010171:Palmitoyl Coenzyme A; D009288:Naproxen; D007660:Ketoprofen; D003066:Coenzyme A Ligases; C090799:FAA2 protein, S cerevisiae; D000098859:Long-Chain-Fatty-Acid-CoA Ligase; D005279:Fenoprofen; D007052:Ibuprofen