Comparisons Between the Kinetic Behaviour of the Muscle Carnitine Palmitoyltransferase I of a Higher and Lower Vertebrate

Abstract

The Vmax of rat muscle mitochondrial CPT I toward the coenzyme A derivatives of 16:0, 16:1n-7, 18:1n-9, and 22:6n-3 were far lower than those recorded previously for this enzyme in rat liver at the same temperature (37°C). However, the Vmax of 7.0 nmol · min−1 · mg mitochondrial protein−1 for linoleoyl CoA (18:2n-6), which was the greatest recorded for the five acyl CoAs examined in muscle, was similar to that in liver. These comparisons presumably reflect a difference in the essential fatty acid requirements of these two rat tissues. Although the Vmax values for CPT I in the musculature of a lower vertebrate (larval lamprey) at 20°C were similar to those exhibited toward the coenzyme A derivatives of 16:0, 16:1n-7, 18:1n-9, and 22:6n-3 by the CPT I of rat musculature at 37°C, the corresponding Vmax toward 18:2n-6 (3.2 nmol · min−1 · mg mitochondrial protein−1) was lower. The latter relatively low activity may spare from oxidation this essential fatty acid, which is in low abundance in the diet of larval lampreys. Although the Vmax values toward the four nonessential fatty acids in larval lamprey muscle were similar to those in rat muscle, the corresponding K0.5 values were lower, thus indicating that the musculature of larval lampreys has a high capacity for energy generation through β-oxidation.