EFFECT OF FATTY‐ACID DOUBLE‐BOND POSITION ON THE SELECTIVITY OF RAT‐BRAIN ENZYMES: THE INCORPORATION OF OLEIC AND CIS‐VACCENIC ACIDS INTO LYSOLECITHIN IN VITRO

Publisher Website
Google Scholar
Abstract
Abstract— —Selectivity in the esterification of fatty acids to lysolecithin by rat‐brain enzymes in vitro was investigated using free fatty acids (activation plus esterification) and CoA esters (esterification) of two naturally‐occurring monoenoic fatty‐acid isomers, oleic acid [18:1 (n ‐ 9)] and cis‐vaccenic acid [18:1 (n ‐ 7)]. Esterification of free acids to l‐acyl‐sn‐glycero‐3‐phosphorylcholine (1‐acyl GPC) was dependent on CoA and ATP, and was stimulated by MgCl2 and NaF. Under comparable conditions, fatty‐acid activation (acyl‐CoA synthetase [acid: CoA ligase (AMP)] EC 6.2.1.3.) appeared to be rate‐limiting to 1‐acyl GPC acyltransferase (acyl‐CoA:l‐acylglycero‐3‐phosphocholine O‐acyltrans‐ferase, EC 2.3.1.23.), since rates were always less with free fatty acids than with the CoA esters. A comparison of substrate curves obtained with free fatty acids and CoA esters suggests a preference for oleic acid during activation. Acyltransferase activity with 2‐acyl GPC was similar with both acyl‐CoA isomers, whereas with 1‐acyl GPC, activity with oleoyl‐CoA consistently exceeded that with cis‐vaccenoyl‐CoA. This difference between patterns of selectivity in esterification of positions 1 and 2 of lecithin suggests that separate enzymes catalyze the two reactions. The transfer of the isomers to the 2 position was affected in a similar manner by changes in pH and temperature, as well as in protein, fatty acid (or acyl‐CoA), and 1‐acyl GPC concentrations. Patterns of incorporation with simultaneous incubation of both isomers suggests one enzyme. Differences in acyltransferase activity with the two isomerie acyl‐CoA's were observed in subcellular distribution, activity changes with brain maturation, and loss of activity on preincubation of microsomes at 45C. From these results it is not certain whether oleic and cis‐vaccenic acids are esterified to the 2 position by separate enzymes, or by one enzyme with different affinities for the isomers. However, the investigation clearly indicates that acyltransferases, and possibly acyl‐CoA synthetases in brain possess selectivity related to subtle differences in double‐bond position. These selectivities probably are important in determining the specific fatty‐acid composition of the complex lipids of brain.

This publication has 42 references indexed in Scilit: