Lipid biosynthesis in sebaceous glands. Regulation of the synthesis of n- and branched fatty acids by malonyl-coenzyme A decarboxylase

Abstract

Crude cell-free extracts isolated from the uropygial glands of goose catalyzed the carboxylation of propionyl-CoA but not acetyl-CoA. However, a partially purified preparation catalyzed the carboxylation of both substrates and the characteristics of this carboxylase were similar to those reported for chicken liver carboxylase. The Km and Vmax for the carboxylation of either acetyl-CoA or propionyl-CoA were 1.5 times 10- minus-5 M and 0.8 mumol per min per mg, respectively. In the crude extracts an inhibitor of the acetyl-CoA carboxylase activity was detected. The inhibitor was partially purified and identified as a protein that catalyzed the rapid decarboxylation of malonyl-CoA. This enzyme was avidin-insenitive and highly specific for malonyl-CoA with very low rates of decarboxylation for methylmalonyl-CoA and malonic acid. Vmax and Km for malonyl-CoA decarboxylation, at the pH optimum of 9.5, were 12.5 mumol per min per mg and 8 times 10- minus-4 M, respectively. The relative activities of the acetyl-CoA carboxylase and malonyl-CoA decarboxylase were about 4 mumol per min per gland and 70 mumoles per min per gland, respectively. Therefore acetyl-CoA and methylmalonyl-CoA should be the major primer and elongating agent, respectively, present in the gland. The major fatty acid formed from these precursors by the fatty acid synthetase of the gland would be 2,4,6,8-tetramethyl-decanoic acid which is known to be the major fatty acid of the gland (Buckner, J. S. and Kolattukudy, P. E. (1975), Biochemistry, following paper). Therefore it is concluded that the malonyl-CoA decarboxylase controls fatty acid synthesis in this gland.

Chemistry of preen gland secretions of passerines: different pathways to same goal? why?

“…It seems therefore impossible to speculate that they derive these compounds from the diet unless we learn more about their feeding ecology. A few studies have shown that birds can synthesize some of these compounds de novo via several pathways to produce even and odd numbered, and branched acids and alcohols (Buckner & Kolattukudy 1975;Buckner et al 1978;Hiremath et al 1992;Kolattukudy & Rogers 1987). Thus it appears probable that birds have evolved to produce different mixtures to arrive at similar types compounds to perform similar types of functions in response to the ectosymbionts they encounter, but the organisms may be different for different species.…”

Regulation of carnitine palmitoyltransferase activity by malonyl-CoA in mitochondria from sheep liver, a tissue with a low capacity for fatty acid synthesis

“…Methylmalonyl-CoA is an intermediate of propionate metabolism. It can be formed through carboxylation of propionyl-CoA either in the mitochondrial matrix or in the cytosol through the action of propionyl-CoA carboxylase and acetyl-CoA carboxylase (Buckner & Kolattukudy, 1975) respectively. Translocation of the propionyl and methylmalonyl moieties across the mitochondrial inner membrane can be achieved through the formation and transport of their respective carnitine esters.…”

Control Mechanisms in the Synthesis of Saturated Fatty Acids

“…A novel mechanism for controlling the supply of alternate substrates has been described for the uropygial gland of the goose (32,33). Cell-free extracts from this gland catalyze the carboxylation of propionyl-CoA but not of acetyl-CoA, yet a partially purified preparation carboxylates both substrates.…”