FATTY-ACID CELLULAR-METABOLISM AND LACTONE PRODUCTION BY THE YEAST PICHIA-GUILLIERMONDII

Methyl ricinoleate conversion into gamma-decalactone by fungi is alrea dy widely used by the aromatic industry. It offers an interesting alte rnative to chemical synthesis by permitting acquisition of a natural l abel. Peroxisomal beta-oxidation has been described as the probable tr ansformation mechanism. This paper provides information about this met abolism and shows the importance of the step catalysed by carnitine oc tanoyltransferase. After culture of the yeast Pichia guilliermondii on a medium containing methyl ricinoleate as sole carbon source, we conf irmed that mitochondrial beta-oxidation could not be responsible for t he biotransformation. We also observed the effect of chlorpromazine, a n inhibitor of carnitine octanoyltransferase, on peroxisomal beta-oxid ation and therefore on lactone production, and on lipid accumulation b y the yeasts. The presence of chlorpromazine caused a reduction in aro matic specific production yield. This reduction was inversely proporti onal to the amount of chlorpromazine present in the medium. A consider able accumulation of methyl ricinoleate derivatives was also observed. We therefore concluded that the metabolism responsible for the biocon version was peroxisomal beta-oxidation. The effects of chlorpromazine suggested that the entry of fatty acids into the peroxisomes took plac e in a carnitine-dependent manner. This step might be a limiting step in the metabolism.