Lipid synthesis in Lipomyces lipofer

Abstract

The synthesis of lipids by cell-free fractions of Lipomyces lipofer was investigated by measuring the incorporation of acetate-14C and other radioactive precursors into lipid-soluble material. On the basis of cofactor requirements, the reaction to inhibitors, and the ability to incorporate appreciable quantities of malonate-14C, it was concluded that the malonyl-CoA pathway was the principal route of fatty acid synthesis in this yeast. By employing a means of cell dispersion less rigorous than previously used with yeasts, it was shown that the soluble portion (high-speed supernatant) of the cell was primarily involved in lipid synthesis. The mitochondrial fraction and the high-speed pellet (96 000 × g, 1 h) were inactive although the latter fraction was required for the maximum activity of the high-speed supernatant. The stimulatory activity of this pellet was very labile and showed a lag period before it became effective. Several lines of evidence suggested that the carboxylation of acetyl-CoA is the rate-limiting step in lipid synthesis which is accelerated by the high-speed pellet.