Meeting Abstract

44.4  Tuesday, Jan. 5  Fueling flight with fat: substrate selectivity of avian CPT PRICE, Edwin R.*; GUGLIELMO, Christopher G.; University of Western Ontario; University of Western Ontario eprice3@uwo.ca

Carnitine palmitoyl transferase (CPT) catalyzes the conversion of fatty acyl CoA to fatty acyl carnitine which can then be transported across the mitochondrial membrane. This is often considered the rate-limiting step in fatty acid oxidation; preference of CPT toward particular fatty acyl CoA substrates could thus determine maximal rates of fat utilization when different fatty acids are supplied to muscles. We used spectrophotometric assays to examine CPT enzymatic rates when supplied with different fatty acyl CoA substrates using pectoralis muscles from white-throated sparrows (Zonotrichia albicollis). To determine if the CPT selectivity changes with migratory state, we examined captive birds held on a ‘winter’ short day light cycle, as well as those that were photoperiod-stimulated to be in ‘migratory’ condition. Within a chain length, monounsaturates demonstrated higher CPT activity than saturated fatty acids. CPT activity decreased with chain length, with low activity in 18:0 and undetectable activity with 20:0. Within the 18 carbon series, activity was higher with polyunsaturates, although activity of 18:3 was not significantly greater than that of 18:2. Pattern of selectivity did not vary between ‘winter’ and ‘migratory’ birds. The observed pattern of selectivity is similar to that found previously in rats, but the high CPT activity with polyunsaturates contrasts with previous findings in fish. We conclude that the selectivity of CPT can affect maximal rates of fatty acid oxidation, which in turn can affect migratory performance.