The conversion of stearic to oleic acid by liver and yeast preparations

Abstract 1. 1. Rat-liver homogenates, capable of converting stearic acid to oleic acid, were fractionated by differential centrifugation. The isolated microsomes converted stearyl-CoA to oleate in the presence of oxygen and reduced TPN. The supernatant solution contained the stearate-activating enzymes. The oleic acid formed was isolated and degraded and shown to be the natural Δ 9 -isomer by gas-chromatographic identification of the radioactive azelaic acid formed. 2. 2. Rat-liver homogenates, yeast cells, and cell-free yeast extracts which converted stearate to oleate in about 13% yield, all converted 1–2% of the stearate to a hydroxystearic acid. Preliminary results indicated that the product was a mixture of hydroxystearic acids containing both 9- and 10-hydroxstearate as well as several others. 3. 3. The following labelled compounds were incubated with liver homogenates, yeast cells, and cell-free extracts of yeast; 9-hydroxystearic acid, 10-hydroxystearic acid, 9,10-epoxystearic acid, and 9,10-dihydroxystearic acid. The labelled fatty acids produced from these were isolated and measured by gas-liquid chromatography arranged for the automatic counting of each acid. Both 9- and 10-hydroxystearic acids were converted to oleic acid, although in less than 4% yield by all three systems. A second major product formed exhibited the chromatographic behaviour of a monohydroxy mono-unsaturated C 18 acid but was not further identified. In all systems tested, except intact yeast cells, 9- or 10-hydroxystearic acid was also converted to a slight extent (2% or less) to stearic acid. The CoA derivatives of 9- and 10-hydroxystearic acids were not converted to oleate to any greater extent than the free acids. 9,10-Epoxystearic acid was converted to both oleic and stearic acids by liver but not by yeast preparations; while 9,10-dihydroxystearic was inert in both systems. 4. 4. These results support the hypothesis of a hydroxystearic acid as an intermediate in the formation of oleic acid from stearic acid only if it is assumed that the intermediate is irreversibly bound to the enzyme.