Purification and properties of an acid phosphatase from lactating bovine mammary gland

An acid phosphatase was partially purified from the cytosol of lactating bovine mammary gland by precipitation with ammonium sulfate and protamine, chromatography on carboxymethyl cellulose, and gel filtration on Sephadex G-75. The enzyme hydrolyzed aromatic phosphates but was less active toward alkyl phosphates, ATP, and phosphoproteins (casein and phosvitin). A sulfhydryl group seems to be essential for activity, since dithiothreitol and cysteine activated the enzyme; compounds that react with the sulphydryl groups in proteins were inhibitory. Orthovanadate, phosphate, and zinc ions also inhibited the phosphatase.