Specificity in the enzymic conversion of substituted cis-8, cis-11, cis-14-eicosatrienoic acids into prostaglandins

Inhibition of soybean lipoxygenase and mouse skin tumor promotion by onion and garlic components

Onion and garlic essential oils were previously shown to inhibit mouse skin tumor promotion, as were the enzymes, lipoxygenase, and cyclooxygenase. In the present study, the inhibition of soybean lipoxygenase (EC 1.13.11.12) by onion and garlic components and related compounds was investigated. The IC50 values as well as the kinetic inhibition constants were determined for the most active compounds. Di-(1-propenyl) sulfide, an analog of the substrate moiety required for oxygenase action, was the only irreversible inhibitor observed with Ki = 59 microM and k3 = 0.53/min. Inhibition in the presence of substrate was uncompetitive at 88 and 132 microM linoleic acid with Ki = 129 microM. At 173 microM linoleic acid, however, inhibition was competitive with Ki = 66 microM. Dially trisulfide, allyl methyl trisulfide, and diallyl disulfide were competitive inhibitors, while 1-propenylpropyl sulfide and (E, Z)-4,5,9-trithiadodeca-1,6,11-triene 9-oxide (ajoene) were mixed inhibitors. Nordihydroguaiaretic acid (NDGA), the most potent lipoxygenase inhibitor, was a competitive inhibitor with Ki = 0.29 microM. The results indicate a relative potency of inhibition for structural features in the following order: di(1-propenyl) sulfide greater than an alkenyl trisulfide greater than an alkenyl disulfide. Di(n-propyl) disulfide, a major onion oil component, inhibited neither lipoxygenase nor promotion. Di(1-propenyl) sulfide and ajoene inhibited both. This suggests that the inhibition of lipoxygenase may be involved in antipromotion.

Naturally occurring conjugated octadecatrienoic acids are strong inhibitors of prostaglandin biosynthesis

Fatty acids from natural sources (mostly seed oils) were isolated and assayed for their effect on the bioconversion of arachidonic acid into prostaglandin E2, using sheep vesicular gland microsomes. Homologues and isomers of the naturally occurring fatty acids, obtained by chemical modification and/or organic synthetic methods, were also tested. Two very active cyclooxygenase inhibitors were discovered, namely jacarandic acid (8Z, 10E, 12Z-octadecatrienoic acid), isolated from Jacaranda mimosifolia, the concentration which gives 50% inhibition ([I]50) being 2.4 microM and the synthetic 8Z, 10E, 12E-octadecatrienoic acid, having an [I]50 of 1.0 microM. Under the conditions of the assay (75 microM substrate), earlier described potent inhibitors showed the following [I]50's: indomethacin: 1.3 microM; 9,12-octadecadiynoic acid: 1.3 microM, 8Z, 12E, 14Z-eicosatrienoic acid: 2.7 microM; 5,8,11,14-eicosatetraynoic acid: 4.4 microM. At a concentration of about half that of the substrate, the following naturally occurring fatty acids revealed inhibition ([I]50): columbinic acid (29 microM), calendulic acid (31 microM), liagoric acid (31 microM), ximenynic acid (39 microM), crepenynic acid (40 microM) and timnodonic acid (43 microM). Other fatty acids, and some of the above acids, were converted themselves more or less rapidly, mostly into conjugated monohydroxy fatty acids.

On the haemoprotein character of prostaglandin endoperoxide synthetase

Prostaglandin endoperoxide synthetase is a membrane-bound glycoprotein isolated as a dimer of molecular weight of approximately 129 000 consisting of two identical polypeptide chains. Several research workers have reported that haemin (ferri-protoporphyrin-IX) is required to restore the full enzymic activity of the pure apoprotein. Difference spectroscopy shows association of haemin up to two molecules per polypeptide chain of molecular weight 70 000. Both the cyclooxygenase and the peroxidase activity displayed by the enzyme can be optimally stimulated by similar quantities of haemin. The restored haemin-enzyme complex has a millimolar absorption coefficient at 408 nm of 61 mM-1 . cm-1 per haem. Using this value, the presence of non-haem iron in the enzyme is virtually excluded. These findings and the spectra of the reassociated enzyme-haemin complex point to a haemoprotein character. The availability of haemin to the enzyme might play a regulating rôle in its action.

13C-NMR of double and triple bond carbon atoms of unsaturated fatty acid methyl esters

The carbon magnetic resonance spectra of many fatty acid methyl esters with cis and trans double bonds and triple bonds at various positions and in many different combinations have been investigated. The influence of the ester group on double and triple bonds in the fatty acid chain depends strongly on the positions of these bonds. For a given position the influence is constant, even if one or more other double or triple bonds are present. Together with the evaluated chemical shift parameters for the effects of double and triple bonds on each other, complete assignments are possible and spectra of various types of unsaturated esters can be predicted with high accuracy (+/- 0.1 ppm).