Purification and properties of hydroxypyruvate: l-Alanine transaminase from rabbit liver

A procedure is described for the extensive purification of hydroxypyruvate:l-alanine transaminase from rabbit liver. On the basis of gel filtration studies, the molecular weight of the enzyme is estimated to be about 41,000 daltons. A similar value was obtained when the enzyme was subjected to gel electrophoresis in the presence of sodium dodecyl sulfate indicating that the enzyme consists of a single polypeptide chain.The purified enzyme catalyzes the transamination of glyoxylate as well as hydroxypyruvate with l-alanine as the preferred amino donor for both substrates. The two enzymatic activities were not separated during purification nor by Chromatographic or electrophoretic procedures. Kinetic studies demonstrated that the two α-keto acids are competitive substrates. The above data are consistent with the fact that a single enzyme catalyzes the transamination of both glyoxylate and hydroxypyruvate. The effects of various inhibitors on enzymatic activity were investigated. The enzyme is inhibited by glyceraldehyde-3-phosphate and other aldehydes.The possible role of hydroxypyruvate:l-alanine transaminase in gluconeogenesis is discussed.