Multiple forms of barley root acid phosphatase: purification and some characteristics of the major cytoplasmic isoenzyme.

ABSTRACT

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 electrophoresis and moves as a single band of Mr approximately 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 x 10(-7) M). NaF, Ag(+), Hg(2+), Pb(2+) and Zn(2+) 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.