Partial Purification and Properties of Phosphoenolpyruvate-carboxykinase from Castor Bean Endosperm

Abstract

Enzymes catalyzing the reaction between phosphoenolpyruvate (PEP) and oxalacetate (OAA) were investigated with three different kinds of germinating seeds. PEP-carboxy-kinase was found in castor bean endosperm, and PEP-carboxylase in soybean and pea cotyledons.
Activity of PEP-carboxykinase could be detected from the 3 rd day after germination and reached the maximum on the 7 th day seedling of castor bean in the dark at 30°C. This enzyme was extracted from the endosperm of the 7 th day seedling and purified partially. The enzyme required adenine nucleotide and Mn ion for the activity. The optimum pH's were found to be 6.4 for the carboxylation reaction, and 8.4 for the decarboxylation reaction. The chromatographic peak of this enzyme on Sephadex G-200 was devided into two peaks by the addition of Mn ions and the activity curve was sigmoidal with respect to the concentration of MnCl₂, indicating the oligomeric nature of the enzyme. The sigmoidal character of the activity curve was also observed with OAA and ATP, but it decreased with increasing concentration of the enzyme. Consequently, important factors affecting the activity were the concentration of enzyme and substrates.