Acyl-CoA synthetase activity of rat liver microsomes. Substrate specificity with special reference to very-long-chain and isomeric fatty acids.
1. A fatty acid-depleted rat liver microsomal fraction has been used for the measurement of acyl-CoA synthetase (acid : CoA ligase (AMP-forming), EC 6.2.1.3) activity. The assay was based on measurement of the reaction product AMP by high-performance liquid chromatography (HPLC). The synthetase activity (V') revealed an optimum at 12 : 0 with saturated fatty acids as substrate, and at 14 : 1 with mono-unsaturated fatty acids. The apparent Michaelis constant, on the other hand, showed no systematic dependence on the fatty acid chain-length. 2. The mono-unsaturated fatty acids from 14 : 1 to 22 : 1 gave higher activities than the corresponding saturated fatty acids, and the relative differences were greatest with the very-long-chain fatty acids eicosaenoic (20 : 1 (11) (cis)) and docosaenoic acid (22 : 1 (11) (cis)). The synthetase activity with saturated and mono-unsaturated fatty acids was found to correlate to their capacity factor (k') on reversed phase chromatography (HPLC). This finding may indicate that the observed chain-length dependence of the activity largely reflects the partition of the fatty acids between a hydrophobic and a hydrophilic phase. In general, the position of the double bond and the cis/trans configuration had little effect on the V' values except for 22 : 1 (11)(cis) which revealed a 2-fold higher activity tha 22 : 1 (13) (cis). 3. The polyunsaturated fatty acid 22 : 6 (all cis) ;was notably found to be a much better substrate than other C22 fatty acids. 4. The present study does not support the idea of more than a single ATP-dependent acyl-CoA synthetase in the rat liver microsomal fraction.
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003066:Coenzyme A Ligases / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013237:Stereoisomerism; D013379:Substrate Specificity; D000098859:Long-Chain-Fatty-Acid-CoA Ligase
D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D003066:Coenzyme A Ligases; C090799:FAA2 protein, S cerevisiae; D000098859:Long-Chain-Fatty-Acid-CoA Ligase