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INTRODUCTION Among fatty acids with conjugated double bonds, the best known is conjugated linoleic acid (CLA) , a geometric and positional isomer of linoleic acid. CLA has various beneficial effects, including anticarcinogenic, antiobesity and antiallergic properties 1-5). Seed oils from certain plants also include conjugated linolenic acids (CLnAs) , which have a conjugated triene system and are geometrical and positional isomers of α-linolenic acid (LnA, 9c, 12c, 15c-18:3) 6-8) .We have performed several studies of CLnAs, including showing that α-eleostearic acid (α-ESA, 9c, 11t, 13t-18:3) has strong antitumor and antiangiogenic effects

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The time course of hydrogenation of linoleic acid to trans-l l-octadecenoic acid was observed in a growing culture of Treponema (Borrelia) strain B25. A conjugated fatty acid, cis-9, trans-I1-octadecadienoic acid, was identified as an intermediate in the process. The isomerase responsible for the conversion of linoleic acid to the conjugated fatty acid was found to be associated with a particulate fraction characterized by a high protein and lipid content in a 2:1 ratio. Optimum pH for isomerase activity was found to be 7.0 in 0.05 M potassium phosphate buffer. No cofactor requirements could be demonstrated for the isomerase. The sulfhydryl inhibiting agents, iodoacetamide, N-ethylmaleimide, and p-chloromercuribenzoate, inhibited isomerase activity. Isomerase activity was also inhibited by the metal chelators, o-phenanthroline, a, a'-bipyridyl, ethylenediaminetetraacetic acid, and 8-hydroxyquinoline. Linoleic (A9, 12), linolenic (A9, 12, 15), and gamma-linolenic (A6, 9, 12) acids served as effective substrates for the isomerase; however, the derivatives of linoleic and linolenic acid did not. K2HPO4, 75 ml of a mineral solution containing 0.6% KH2PO4, 0.6% (NH4)2SO4, 1.2% NaCI, 0.2% MgSO4-7H20, and 0.2% CaCl2 2H2O, 20 ml of 2.5% cysteine-hydrochloride, and 50 ml of 8% Na2COM. The Na2CO3 solution was autoclaved, aseptically equilibrated with CO2, and added to the medium after sterilization and cooling. Rumen fluid was collected in 6-to 8-liter batches from fistulated cows belonging to the Department of Dairy Science. Large feed particles were removed by 519 on July 5, 2020 by guest http://jb.asm.org/ Downloaded from 526

A number of studies have been conducted to elucidate the properties and mechanism of the hydrogenation of Clg unsaturated fatty acids by rumen microorganisms. Progress in this area has been reviewed by Dawson & Kemp (1970). During screening of a number of pure cultures of rumen bacteria, several species have been shown to hydrogenate linoleate to trans-octadecenoate (Polan,