Abstract

Acetyl-CoA carboxylase (ACC) catalyzes the formation of malnoyl-CoA, which in turn controls the rate of fatty acid metabolism. ACC beta or 2 has been shown to be localized on the mitochondria in close proximity to carnintine palmitoyl transferase 1 (CPT-1), the enzyme responsible for the influx of acyl-CoA into the matrix where beta oxidation takes place. CPT-1 is inhibited by malonyl-CoA produced by ACC. It has been well documented that AMP activated kinase (AMPK) when activated phosphorylates and inactivates ACC. ACC is controlled allosterically by citrate, which activates, and by palmitoyl-COA, which inhibits. In this study, we asked the question, "Does phosphorylation by AMPK effect the inhibition of ACC by palmitoyl-CoA?" ACC was isolated and then subjected to phosphorylation and activity was measured in varying concentrations of acetyl-CoA and citrate. Phosphoryation reduced the substrate (acetyl-CoA) saturation activity curves for ACC at all levels of palmitoyl-CoA. The Ki for palmitoyl-CoA inhibition of ACC was reduced from 1.7 Â± 0.25 ÂµM to 0.85 Â± 0.13 uM (p<0.05) as a consequence of phosphorylation. In addition the citrate activation curves for ACC were greatly reduced in the presence of palmitoyl-CoA. The data show that skeletal muscle ACC or ACC-beta is more potently inhibited by palmitoyl-CoA after phosphorylation by AMPK. During long-term exercise when AMPK is activated and muscle palmitoyl-CoA is elevated this may contribute to the low malonyl-CoA and increased fatty acid oxidation.

Degree

College and Department

Life Sciences; Physiology and Developmental Biology

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