A protein complex capable of methylcrotonoyl-CoA carboxylase activity. In mammals, it is a mitochondrial complex comprising a dodecamer of 6 alpha and 6 beta subunits: MCCC-alpha has a covalently bound biotin essential for the ATP-dependent carboxylation; MCCC-beta possesses carboxyltransferase activity which presumably is essential for binding to 3-methylcrotonyl-CoA.
methylcrotonoyl-CoA carboxylase complex