Purification and characterisation of the pyruvate decarboxylase from a haploid strain of Saccharomyces cerevisiae

A novel purification procedure was developed for pyruvate decarboxylase (PDC, E.C. 1.1.1.4) from the haploid yeast strain YSH 4.127-1A expressing only one (PDC1) of the three structural genes for PDC. The purified enzyme is homotetrameric with a molecular mass of about 240 000 whereas PDC from brewer's yeast is a dimer of dimers composed of subunits of different size (alpha(2) beta(2)) with the same molecular mass as the tetramer. Despite these structural variations there are no significant differences in the kinetic behaviour of the two enzyme species. PDC purified from the haploid yeast mutants shows a sigmoid dependence of the reaction rate from the substrate concentration due to the substrate activation. In the presence of the substrate surrogate pyruvamide the shape of the v/S plot is transformed into a hyperbolic one. As expected, polyclonal antibodies react with both the enzyme from haploid yeast strain mutants and that from brewer's yeast.