Pyruvate carboxylase: the amino acid sequence at the biotin-attachment site of the enzymes isolated from chicken, turkey and sheep liver [proceedings].

Although the physical, chemical and kinetic properties as well as the biological function of pyruvate carboxylase have been studied in detail (for review see Utter et al., 1975), no reports have been published so far on the primary structure of this enzyme. This may be due in part to the large size of the molecule since the vertebrate enzyme appears to be a tetramer consisting of four apparently identical polypeptide chains, each of mol.wt. 110000-125000 and each containing a single covalently attached biotin (Barden et a[., 1975). Nevertheless, information on the amino acid sequence around the biotin molecule would be of particular value for three reasons. (1) It could lead to an understanding of the role of the various amino acid side chains in the functioning of biotin as the carboxyl carrier. (2) A knowledge of the amino acid sequence around the biotin could lead to an understanding of the basis of recognition by the enzyme system that attaches the biotin to the apoenzyme. The final step in the synthesis of biotin-containing enzymes is the covalent attachment of the prosthetic group to the apoenzyme (for review see Moss & Lane, 1971). The holoenzyme synthetase must be able to recognize the apoenzyme and then specifically attach the biotin to the correct lysine residue. Furthermore it has been demonstrated that certain holoenzyme synthetase preparations are capable of the recognition and specific covalent attachment to apoenzymes from bacterial, yeast and vertebrate sources (Kosow et af., 1962; McCallister &Coon, 1965), suggesting that a common structure at the attachment site may be a common feature of many biotin enzymes. (3) The degree of conservation of sequence around biotin may provide insight into the evolution of biotin enzymes and in particular, by comparison with the bacterial enzyme sequences, provide further evidence for the evolution from an ancestral precursor by gene fusion (Obermayer & Lynen, 1976).