A. T. James

The biosynthesis of long-chain fatty acids by lettuce chloroplast preparations

Abstract 1. 1. It is demonstrated that the major site of biosynthesis of saturated fatty acids from C10 to C18 and of oleic acid in leaves is the chloroplast. 2. 2. The co-factors required in the presence of light are ATP, CoA, Mg2+, CO2 and inorganic phosphate. 3. 3. In the dark greatly diminished synthesis occurs despite the presence of a full complement of cofactors. 4. 4. As in photosynthetic phosphorylation the synthesis of fatty acids is inhibited by NH3 and 3(p-chlorophenyl) 1,1-dimethyl urea but not by dinitrophenol. 5. 5. Under anaerobic conditions the biosynthesis of oleic acid drops markedly but that of the saturated acids is relatively unaffected. 6. 6. Isolated chloroplasts are less effective in utilising the C8, C10, C12 and C14 saturated fatty acids for the biosynthesis of oleic acid than is the intact leaf. Both malonic and acetic acids are, however, readily utilised.

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

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 Δ9-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 C18 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.

The biosynthesis of long-chain saturated and unsaturated fatty acids in isolated plant leaves

Abstract 1. 1. The incorporation of labelled acetic, octanoic, decanoic, dodecanoic, tetradecanoic, hexadecanoic, octadecanoic and 9-octadecenoic acids into the saturated and unsaturated fatty acids of lipids from isolated leaves (mainly Ricinus communis ) is described. 2. 2. With the exception of hexadecanoic and octadecanoic acids all these labelled compounds acr as precursors of oleic, linoleic and linolenic acids. 3. 3. Hexadecanoic and octadecanoic acids are incorporated into leaf lipids. 4. 4. In the absence of oxygen no oleic acid is synthesized. 5. 5. Two separate pools of the longer-chain fatty acids are suggested. In one myristic acid is converted to palmitic and stearic acids which are then esterified to give galactolipid and phosopholipid. In the second pool myristic acid is converted to palmatic acid, then to stearic acid and finally to oleic acid. Only the latter is freely available for esterification to combined lipids or for conversion to linoleic and linolenic acids.

The influence of diet on the quality of faecal fat in patients with and without steatorrhoea

By the use of gas-liquid chromatography it has been shown that the quality of the faecal fat in individuals without steatorrhoea is little affected by changes in the quality of the dietary fat. Large amounts of non-dietary fatty acids have been identified in the faeces both of patients with and without steatorrhoea. These have been identified as a number of isomers of oleic acid and hydroxystearic acids, particularly 10-hydroxystearic acid.

In vitro lipid synthesis in fowl blood

Abstract 1. 1. Fowl whole blood has been shown to incorporate labelled acetate into both cellular and plasma lipids. 2. 2. Long chain saturated and unsaturated acids are shown to be synthesized and then incorporated into triglycerides, phospholipids and cholesterol esters. 3. 3. “Sterol”-like unsaponifiable substances are also synthesized from acetate. 4. 4. Comparison of the synthetic ability of leucocytes, young erythrocytes and old erythrocytes show that all cells contribute to the synthesis, the most active being the leucocyte and young erythrocyte preparations.