Glyoxysomal β-oxidation of long-chain fatty acids:: completeness of degradation

The ability of glyoxysomes from sunflower (Helianthus annuus L.) cotyledons to completely degrade long-chain fatty acids into their constituent acetyl units and the time courses of the appearance of acyl-CoA intermediates during beta-oxidation have been studied using C-14-labelled substrates at non-saturating concentrations (1.3 to 1.8 mu mol.l(-1)). [C-14]Acetyl-CoA was formed from [18-C-14]oleate metabolized at a yield of up to 80%, and from [U-C-14]palmitate and [U-C-14]linoleate to an extent indicating that a maximum of 80% and 30%, respectively, of the substrate P-oxidized had been degraded beyond the C-4-CoA intermediate level. To obtain the latter values, an acetyl-CoA-removing system was required during beta-oxidation. Constant re-oxidation of the NADH formed during the beta-oxidation did not replace the effect of acetyl-CoA removal. Neither the completeness of the linoleate beta-oxidation nor the rate of reaction were influenced by NADPH. Medium- and short-chain acyl-CoA intermediates were predominantly detected during beta-oxidation of the long-chain substrates employed. The degradation of these intermediates appeared to be stimulated mainly in the presence of an acetyl-CoA-removing system. The time courses of the appearance of intermediates corresponded to a precursor-product relationship between intermediates of decreasing chain lengths.