Some properties of two aldolases in extracts of Aspergillus oryzae

Fructose 1,6-diphosphate (FDP) aldolase and 2-keto-3-deoxy-D-gluconate (KDG) aldolase the two key enzymes of Embden-Meyerhof-Parnas (EMP) and the nonphosphorolytic Entner-Doudoroff (ED) pathways respectively, were identified in cell-free extracts of four Aspergillus oryzae strains grown on D-glucose as sole source of carbon. A. oryzae NRRL 3435 gave the highest enzymatic activity for the two enzymes and selected for further studies. Studies on the properties of the two key enzymes indicated that the optimum conditions for the activities of FDP aldolase and KDG aldolases occurred at pH 8.5, 45 degrees C and pH 8.0, 55 degrees C, respectively. Tris-acetate buffer and phosphate buffer showed the highest enzymatic activity for these two enzymes respectively. KDG aldolase was stable at 55 degrees C for 60 minutes however FDP aldolase was found to be less stable above 45 degrees C. On the other hand the two aldolases showed a high degree of stability towards frequent freezing and thawing. Dialysis of the extracts caused a decrease in the enzymatic activity of KDG aldolase, and an increase in FDP aldolase activity. The addition of ethylene diamine tetraacetate to the crude extracts caused an inhibition of KDG aldolase, whileas FDP aldolase was not affected. Addition of MnCl(2), CoSO(4), MgCl(2) and ZnSO(4) to the dialyzed extracts increased the activity of KDG aldolase by 67%, 54%, 61% and 37%, respectively. On the other hand the addition of some metal salts caused an inhibition of FDP aldolase. The results obtained indicate the absence of evidence for the involvement of sulfhydryl groups in the catalytic sites of the two aldolases.