THE ACTIVITY OF PARTIAL REACTIONS IN THE CHAIN ELONGATION OF PALMITOYL‐CoA AND STEAROYL‐CoA BY MOUSE BRAIN MICROSOMES

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Abstract
Partial reactions in the overall chain elongation of palmitoyl‐CoA and stearoyl‐CoA by mouse brain microsomes have been analyzed. The rate of the initial condensation reaction between palmitoyl‐CoA and malonyl‐CoA was more than 5 times greater than the rate obtained with stearoyl‐CoA, and in both cases good agreement between condensation and overall chain elongation rates was observed.By contrast, both β‐hydroxyoctadecanoyl‐CoA and β‐hydroxyeicosanoyl‐CoA were quite rapidly dehydrated by brain microsomes at similar rates. Similar results were obtained with 2‐trans‐octadecenoyl‐CoA and 2‐trans‐eicosenoyl‐CoA in which both substrates were rapidly reduced at nearly the same rate in the presence of NADPH. In all cases, intermediate reactions subsequent to condensation were much more rapid than overall chain elongation. These results suggest that the mechanism of malonyl‐CoA‐dependent fatty acid chain elongation in brain microsomes is similar to that observed in other tissues, and are consistent with an overall regulation of chain elongation mediated primarily by the initial condensation reaction.