COLD-ACCLIMATION INCREASES CARNITINE PALMITOYLTRANSFERASE-I ACTIVITY IN OXIDATIVE MUSCLE OF STRIPED BASS

Cold acclimation increases carnitine palmitoyltransferase I activity i n oxidative muscle of striped bass. Am. J. Physiol. 266 (Regulatory In tegrative Comp. Physiol. 35): R405-R412, 1994. - The effect of thermal acclimation on the activity of carnitine palmitoyltransferase I (CPT I), the rate-limiting enzyme for P-oxidation of long-chain fatty acids , was determined in oxidative red muscle of striped bass (Morone saxat ilis) acclimated at 5 or 25 degrees C. As observed in mammalian tissue s, malonyl-CoA potently inhibited CPT I activity of mitochondria. Inhi bition by malonyl-CoA required inclusions of both bovine serum albumin (BSA) and palmitoyl-CoA in the reaction media. Because BSA binds long -chain fatty acyl-CoAs, this observation suggests that free fatty acyl -CoAs may disrupt mitochondrial membranes and affect the CPT I protein . Cold acclimation increased citrate synthase activity 1.6-fold and to tal CPT activity 2-fold in homogenates of red muscle; free carnitine i ncreased 62%, and specific activity of CPT I in mitochondria increased 2-fold. No differences were observed between cold- and warm-acclimate d fish in substrate-binding properties of CPT I at an assay temperatur e of 15 degrees C, as judged by the Michaelis constant (K-m) for carni tine (0.11 +/- 0.02 vs. 0.13 +/- 0.02 mM) or inhibition of CPT I, as d etermined by the half-maximal inhibition concentration (IC50) for malo nyl-CoA (0.14 +/- 0.05 vs. 0.09 +/- 0.03 mu M). Thermal sensitivity of CPT I (Q(10) = 2.91 +/- 0.12 vs. 3.02 +/- 0.20) and preference of CPT I for different long-chain fatty acyl-CoA substrates (16:1-CoA = 16:0 -CoA > 18:1-CoA) were not altered by thermal acclimation. We conclude that capacity for oxidation of fatty acids by red muscle from striped bass is increased after cold acclimation primarily by proliferation of mitochondria, without altering the kinetic properties of CPT I.