PURIFICATION OF OXALACETIC CARBOXYLASE FROM CHICKEN LIVER

Abstract

The present investigation was undertaken in an attempt to elucidate the relationship of the fixation of CO2 in OAA’ by OAA carboxylase to that in malate catalyzed by “malic” enzyme. It was hoped that protein separation procedures would demonstrate the identity or non-identity of the two enzyme systems and that in addition purification of the carboxylase might lead to a better understanding of its mechanism. The exchange of isotopically labeled CO2 with OAA was first demonstrated by Krampitz .et al. (1) with preparations of Micrococcus lysodeikticus. Later it was found that pigeon liver extracts catalyzed a similar reaction, but that the reaction in crude extracts required the presence of ATP (2), while the bacterial reaction did not (3). In a separate line of investigation Ochoa and his coworkers (4, 5) showed that pigeon liver also contained an enzyme or enzymes catalyzin, 0‘ the reversible oxidation of malate to pyruvate and CO2 in the presence of TPN. In a study of the possible relationship of these two CO*-fixing mechanisms in crude pigeon liver extracts Utter concluded, on the basis of relative rates of incorporat.ion of Cl4 into pools of malate and OAA, that the incorporation of CO* into OAA as catalyzed by ATP did not involve malate as an intermediate and that, conversely, the fixation into malate with TPN did not involve OAA as a precursor (6). Veiga Salles et al. (7) also demonstrated by means of partially purified “malic” enzyme that OAA was not a precursor of ma1at.e. However, certain considerations of the total amount of COZ fixed in the crude liver extracts under various conditions led to the suggestion (6) that the two fixation reactions might have an unknown common precursor and hence involve a common pathway, at least in part, and this suggestion has also been made by Ochoa (8).