Tartrate-Inhibitable Acid Phosphatase. Purification from Placenta, Characterization and Subcellular Distribution in Fibroblasts

Abstract

Tartrate-inhibitable acid phosphatase was purified to apparent homogeneity from human placenta. The enzyme is composed of 2 subunits with an apparent MW of 48 kDa [kilodalton]. Each subunit carries 1 oligosaccharide of the high-mannose/hybride type. The purified enzyme has an isoelectric point of pH 6.2. It cleaves phosphomonoester bonds at acid pH, is competitively inhibited by L-tartrate, Ki = 0.51 .mu.M, and phosphate, Ki = 0.8mM. A monospecific antiserum raised against the purified placental enzyme precipitated 64% and 85% of the tartrate-inhibitable acid phosphatase present in extracts of placenta and fibroblasts, respectively. By means of subcellular fractionation and immunoprecipitation it was shown that the majority of tartrate-inhibitable acid phosphatase is located in lysosomes in normal and mucolipidosis II fibroblasts. In the human Hep G-2 hepatoma cells a significant fraction of the enzyme appears to be associated with nonlysosomal organelles.