ISOLATION AND CHARACTERIZATION OF A GROUP-III ISOZYME OF ACID-PHOSPHATASE FROM RICE PLANTS

The acid phosphatases (EC 3. 1. 3. 2.) of rice seedlings consisted of four groups of isozymes. The group III isozyme was purified through am monium sulfate, DEAE-Sepharose, Con A-Sepharose, and chromatofocusing. A 198-fold enhancement of activity was attained. This isozyme showed only one band in native-polyacryamide gel electrophoresis. However, ge l filtration revealed two peaks of enzyme activity. Their molecular we ights were 130 kDa and 100 kDa. The purified isozyme showed a pH optim um of 5. Its Km for p-nitrophenyl phosphate (p-NPP) hydrolysis was 0.3 3 mM. Its activity was inhibited non-competitively by sodium fluoride. Mercuric chloride, sodium molybdate, and copper sulfate strongly inhi bited the enzyme activity. The isozyme actively hydrolyzed adenosine t riphosphate and p-NPP, and partially utilized fructose-1,6-diphosphate . It did not utilize fructose-6-phosphate, glucose-1-phosphate, glucos e-6-phosphate, glycerophosphate, or adenosine monophosphate.