Malonyl-CoA decarboxylase from the uropygial gland of waterfowl: purification, properties, immunological comparison, and role in regulating the synthesis of multimethyl-branched fatty acids.

Analysis of the acyl portion of the wax from the uropygial gland of muscovy duck, wood duck, (Cairininae subfamily) and Canadian goose (Anserinae) by combined gas-liquid chromatography and mass spectrometry showed that 2,4,6-trimethyloctanoic acid and 2,4,6-trimethylnonanoic acid were the major (~100%) components. Similar analyses of the wax from the glands of mallard and Peking duck (Anatinae) showed that 2- and 4-mono-methylhexanoic acids predominated (>75%) with no multimethyl-branched acids. The uropygial glands of the former group contained 20 to 100 times as much malonyl-CoA decarboxylase activity as those of the latter group. These results strongly support the hypothesis that this decarboxylase, by causing specific decarboxylation of malonyl-CoA, makes available only methylmalonyl-CoA for fatty acid synthesis, and thus causes the production of multimethyl-branched acids. Malonyl-CoA decarboxylase was purified to apparent homogeniety in 30% yield from the uropygial glands of muscovy and wood ducks. Properties of the enzyme from the ducks, such as S_20.w (7.8 S), molecular weight (190,000) subunit composition (4 × 47,000), amino acid composition, strict substrate specificity, pH optimum (~9.0), K_m (~33 μm), V (~80 μmol/min/mg), and inhibition by SH-directed reagents were similar to those observed with the decarboxylase from the domestic goose. Antiserum prepared against the goose enzyme cross-reacted with and inhibited the decarboxylase from the four genera of ducks and Canadian goose. Ouchterlony double-diffusion analyses showed fusion of precipitant lines with the enzyme from muscovy, wood duck, and Canadian goose, whereas spurs were observed with the enzymes from mallard and Peking ducks. Immunoelectrophoresis showed that the decarboxylases from muscovy and wood ducks were similar and that they were different from the enzyme from the domestic goose. It appears that during evolution, the subfamilies (Anserinae and Cairininae) which synthesize multimethyl-branched acids acquired the ability to produce a high level of malonyl-CoA decarboxylase, an enzyme which is also present in low levels in other organisms.