Abstract
Varieties of pyruvate carboxylase [pyruvate: CO2 ligase (ADP-forming), EC 6.4.1.1] obtained from the livers of several species of vertebrates, including humans, all show the same basic structure. They are composed of large polypeptide chains of molecular weights ranging from 1.2 to 1.3 X 10(5) for the different varieties of the enzyme. The native form of the enzyme appears to be a tetramer with a molecular weight of about 5 X 10(5). In the case of pyruvate carboxylase from chicken liver each polypeptide chain contains a biotin moiety, thus supporting the thesis that the tetramer contains four identical polypeptide chains. Pyruvate carboxylase from yeast appears to be basically similar to those from the vertebrate species and has a tetrameric structure. Each protomer contains a single polypeptide chain with a molecular weitht of 1.25 X 10(5). In contrast, pyruvate carboxylase from two bacterial species, Pseudomonas citronellolis and Axotobacter vinelandii, appears to be a dimer with a molecular weight (2.5 X 10(5)) about half that of the animal and yeast species. As a further difference, each of the protomers of the bacterial enzymes contain two polypeptides of 6.5 and 5.4 X 10(5) molecular weight in case of the Pseudomonas enzyme. The larger of the two polypeptides contains the biotin moiety. The functional units of the bacterial enzyme thus appear to contain two polypeptides while that of the liver and yeast enzymes is made up of a single chain. Neither of these arrangements corresponds with those of other biotin enzymes whose structure has been extensively studied (acetyl-CoA carboxylases from liver or Excherichia coli, and transcarboxylase from Propionibacterium).