PARTIAL-PURIFICATION AND KINETIC-PROPERTIES OF HUMAN PLACENTAL CYTOSOLIC ASPARTATE-TRANSAMINASE

Human placental cytoplasmic aspartate transaminase was purified 404-fo ld by heat treatment, ammonium sulfate fractionation, dialysis and DEA E-Sephadex chromatography. The pH optimum of the enzyme was 6.8 in eit her phosphate or cacodylate buffer, The K-m values of alpha-ketoglutar ate and L-aspartate were 2.06 and 22.5 mM, respectively, A 78% inhibit ion of the enzyme was noted at 4 mM concentration of maleate which inh ibited the enzyme upon competing with alpha-ketoglutarate with a K-i v alue of 1.72 mM, The kinetic properties of this enzyme are compared wi th those of the enzyme from various mammalian and other sources, The d ata are discussed in terms of the probable effectiveness of this enzym e in catabolizing L-aspartate in placenta especially after the consump tion of a high protein diet by the pregnant mother.