PHOSPHOENOLPYRUVATE CARBOXYLASE IN AVOCADO FRUIT - PURIFICATION AND PROPERTIES

Phosphoenolpyruvate carboxylase (PEPC) was extracted from the pericarp of pre-climacteric avocado (Persea americana) fruit and purified typi cally 25-fold. The enzyme displayed maximum activity above pH 7.8. Glu cose-6-phosphate (Glc-6-P) stimulated activity up to five-fold only be tween pH 6.5 and 7.0 with a maximum at pH 6.8, the stimulation curve d iffering from those reported for the enzyme from C4 or CAM photosynthe tic leaves. At pH 6.8, the avocado fruit enzyme was inhibited 50% by 1 0 muM L-malate and the inhibition was partially reversed by Glc-6-P. T he pH sensitivity of avocado fruit PEPC to, respectively, Glc-6-P or L -malate may be an important regulatory function in glycolysis or maint enance of pH in the cytoplasm of the fruit.