| Abstract: | Phosphoenolpyruvate (PEP) carboxylase was purified over 400-fold from Plasmodium berghei. The purified enzyme was stable in 0.4 m potassium phosphate buffer (pH 7.4) containing 0.5 m glucose, 1 mm ethylenediaminetetraacetic acid (EDTA), and 1 mm MgCl(2). It had a molecular weight of 280,000 determined by sucrose density gradient centrifugation in this buffer, but it aggregated and was unstable in the presence of different salts or a more dilute solution of potassium phosphate. The K(m) for PEP was 2.6 mm and that for Mg(2+) was 1.3 mm. The K(m) for bicarbonate was 2 mm. Citrate, nucleotides, and EDTA inhibited the PEP carboxylase of P. berghei by decreasing the concentration of free magnesium ions, but acetyl-coenzyme A, fructose-1,6-diphosphate, and aspartate did not influence its activity. A chloroquine concentration of 1.8 x 10(-4)m inhibited the enzyme 50%. |
