MULTIPLE FORMS OF BARLEY ROOT ACID-PHOSPHATASE - PURIFICATION AND SOME CHARACTERISTICS OF THE MAJOR CYTOPLASMIC ISOENZYME

The major acid phosphatase form (orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2) was purified from the soluble extract of barley roots. The enzyme is homogeneous on polyacrylamide gel electroporesis and moves as a single hand of Mr ∼ 38 000 in the presence of sodium dodecyl sulphate. The molecular weight of the native enzyme was Mr 77 600 and 79 000 as determined, respectively, by gel filtration on a Sephadex G-100 column and by density gradient ultracentrifugation. The isoelectric point was about 6.28. The enzyme is competitively inhibited by molybdate (Ki = 9 · 10-7 M). NaF, Ag+, Hg2+, Pb2+ and Zn2+ are also inhibitors, while other cations showed no effect. The enzyme hydrolyzes a wide variety of natural and synthetic phosphate esters. In particular, the enzyme seems to be active on ATP, o-phosphotyrosine, o-phosphoserine and glucose 1-phosphate. The pH dependence studies between pH 4-8 using p-nitrophenylphosphate as substrate and diethylpyrocarbonate inactivation indicate the presence of essential histidine residue at the active site. © 1990.