Donald T. Downing

Photodensitometry in the thin-layer chromatographic analysis of neutral lipids.

Abstract A procedure for photodensitometric quantitation of thin-layer chromatograms is described which can give a complete analysis of a mixture of neutral lipids in a single chromatogram without the necessity for reference mixtures.

Enzyme inhibition by acetylenic compounds.

Abstract Soybean lipoxidase and prostaglandin synthetase from sheep seminal vesicles are subject to powerful inhibition by 5,8,11,14-eicosatetraynoic acid, apparently by a slow but irreversible attack on the enzymes. It is postulated that inhibition may result from conversion of the acetylenic compound to a reactive allene by the enzymes studied, as has been proposed in the inhibition of β-hydroxydecanoyl thioester dehydrase by 3-decynoyl-N-acetylcysteamine.

Inhibition of prostaglandin biosynthesis by eicosa-5,8,11,14-tetraynoic acid

Abstract Conversion of arachidonic acid to prostaglandin E 2 by acetone powders of sheep seminal vesicles was irreversibly inhibited by low concentrations of eicosa-5,8,11,14-tetraynoic acid. This compound also inhibited the hydroxylation of linoleic and linolenic acids by the tissue preparation, thereby preventing the elimination of the inhibitory effects of these polyethylenic acids. The tetraacetylenic acid can therefore limit prostaglandin biosynthesis both by its direct effect on prostaglandin synthetase and by preventing the inactivation of endogenous inhibitors.

Rapid determination of double-bond positions in monoenoic fatty acids by periodate-permanganate oxidation

Tetramethylammonium hydroxide has been used in the extraction and pyrolysis methylation of the carboxylic acids produced by periodate-permanganate oxidation of monounsaturated fatty acid methyl esters. This modification of the von Rudloff procedure allows rapid determination of double-bond positions and analysis of mixtures of positional isomers of monoenoic fatty acids.

Structural requirements of acetylenic fatty acids for inhibition of soybean lipoxygenase and prostaglandin synthetase

The conversion of linoleic acid to its hydroperoxide by soybean lipoxygenase and the conversion of arachidonic acid to prostaglandin E2 by a preparation of sheep seminal vesicles, both previously shown to be irreversibly inhibited by eicosa-5,8,11, 14-tetraynoic acid, are similarly inhibited by octadeca-9,12-diynoic acid. No other member of a series of ten diynoic fatty acids, nor any of fifteen positional isomers of octadecynoic acid, showed detectable inhibition. Of a group of four isomeric octadecenynoic acids, having one acetylenic and either a cis- or trans-ethylenic bond in the 9 or 12 positions, none significantly inhibited soybean lipoxygenase, whereas only one, octadec-cis-9-en-12-ynoic acid failed to strongly inhibit prostaglandin synthesis.

Skin surface lipids of the guinea pig

Skin surface lipids of the guinea pig were found to contain sterol esters (33%), wax diesters (diacyl alkanediols) (24%), glycerol ether diesters (28%), free fatty alcohols (6%) and free sterols (9%). The sterol esters and diacyl alkanediols contained saturated fatty acids (40 and 67%, respectively) having straight and singly-branched chains and mono-unsaturated acids (60 and 33%,respectively) derived predominantly by delta 9-desaturation of C15 and C16 straight-chain saturated fatty-acid precursors. The 1-O-alkylglycerols and fatty acids from the glycerol ether diesters were both entirely saturated series containing straight, branched and multi-branched chains. Both the free and the esterified sterols consisted principally of cholesterol with a small proportion of lathosterol.

Unsaturated fatty acid effect on cyclic amp levels in human embryo lung fibroblasts

The addition of arachidonic acid at 250 muM to cultures of human embryo lung fibroblasts (IMR-90) increases cellular cyclic AMP levels within 5 minutes to approximately 15-fold over basal. Other unsaturated fatty acids, 11, 14, 17-eicosatrienoic, linoleic, 8, 11, 14-eicosatrienoic and oleic also cause similar rapid elevation of cellular cyclic AMP. During this time interval, no detectable conversion of the added linoleic or arachidonic acids to prostaglandin is observed. These cells produce prostaglandins at measurable concentrations in response to treatment with ascorbic acid or bradykinin. Saturated fatty acids have no influence on cyclic AMP levels in these cells. This effect of unsaturated fatty acids on cellular cyclic AMP levels varies with the cell type. For example, smooth muscle and endothelial cells obtained from the calf pulmonary artery show very little or no increase in cellular cyclic AMP upon exposure to arachidonic acid.

Differential inhibition of prostaglandin synthetase and soybean lipoxygenase

Abstract Similarity between the primary active sites of soybean lipoxygenase and prostaglandin synthetase is evidenced by the similarity of their fatty acid substrates, by the identical points at which the substrates are atacked for the subsequent insertion of molecular oxygen, and by the observations that both enzymes are irreversibly inhibited by eicosa-5,8,11,14-tetraynoic acid and by octadeca-9,12-diynoic acid. However, several octadecenynoic acids inhibit prostaglandin synthetase but not soybean lipoxygenase. It has now been found that indomethacin, while inhibiting the initial attack on arachidonic acid catalysed by prostaglandin synthetase, is inactive against soybean lipoxygenase. These observations indicate that the soybean enzyme is of limited value as a model for the study of prostaglandin synthetase or as a means of identifying inhibitors of prostaglandin synthesis.