Inhibition studies on acetyl group incorporation into chloroplast fatty acids

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Abstract
Whilst L‐acetylcarnitine acted as a substrate for fatty acid synthesis by isolated pea leaf chloroplasts, D‐acetylcarnitine did not. This result, together with those obtained using the inhibitors D‐carnitine and deoxycarnitine, indicated that L‐acetylcarnitine was not being hydrolysed to free acetate prior to incorporation into chloroplast fatty acids. Seventy‐five per cent and 66% inhibitions of L‐acetylcarnitine incorporation into fatty acids, brought about by adding equimolar quantities of D‐carnitine and deoxycarnitine, respectively, were suggestive of competitive inhibition at two points: an integral membrane translocator in the chloroplast envelope: and the carnitine acetyltransferase enzyme of the chloroplast stroma, which converts L‐acetylcarnitine to acetyl CoA. Isotope competition experiments between acetate and L‐acetylcarnitine confirmed that L‐acetylcarnitine was the preferred substrate for pea chloroplast fatty acid synthesis.