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 typically 25-fold. The enzyme displayed maximum activity above pH 7.8. Glucose-6-phosphate (Glc-6-P) stimulated activity up to five-fold only between pH 6.5 and 7.0 with a maximum at pH 6.8, the stimulation curve differing from those reported for the enzyme from C4 or CAM photosynthetic leaves. At pH 6.8, the avocado fruit enzyme was inhibited 50% by 10 muM L-malate and the inhibition was partially reversed by Glc-6-P. The pH sensitivity of avocado fruit PEPC to, respectively, Glc-6-P or L-malate may be an important regulatory function in glycolysis or maintenance of pH in the cytoplasm of the fruit.