Kinetic behavior of muscle carnitine palmitoyltransferase I in the lampreyGeotria australis, before and after the marine trophic phase

This study was aimed at determining whether the marked changes that occur in the diet during the life cycle of the lamprey Geotria australis, and thus also in the fatty acid composition of the triacylglycerol stores, are accompanied by alterations in the νmax and apparent K0.5 of skeletal muscle carnitine palmitoyltransferase I (CPT I) towards the CoA derivatives of the fatty acids 16:0, 16:1n-7, 18:1n-9, 18:2n-6, and 22:6n-3. The activity of CPT I towards the last four of these acyl CoAs increased progressively from the microphagous larvae to young adults, prior to the onset of their marine trophic phase, to fully grown adults, which had ceased feeding on fish and embarked on their spawning run. For example, the νmax of CPT I towards 18:1n-9 rose from 4.4, to 7.6 to 11.5 nmol · min–1 · mg mitochondrial protein–1 over the course of the three life-cycle stages. The values for the νmax of lamprey muscle CPT I towards the various CoA esters were not directly correlated with the percentage contributions of the corresponding fatty acids to the triacylglycerol stores. Despite very pronounced differences in the biochemistry, physiology, and physical activity of each life-cycle stage, as well as in the fatty acid composition of the triacylglycerols, before and after the adult trophic phase, the νmax for CPT I was always greatest for 16:1n-7 and 18:1n-9. Because the reactivity of CPT I towards the latter two monoenoic fatty acids is also high in teleost fishes and in rat, such a characteristic may have been conserved throughout vertebrate evolution. J. Exp. Zool. 281:6–11, 1998.