Characterization of lysosomal acid phosphatase from normal and malignant mammary tissue.

Acid phosphatase (EC 3.1.3.2) isoenzyme 3 was purified from normal and malignant human mammary tissue and its properties in each were compared. The relative molecular mass of each was 53 000, as measured by sodium dodecyl sulfate gel electrophoresis. Several phosphomonoesters are good substrates for the isoenzymes, whereas organic and inorganic pyrophosphates and phosphoryl choline are hydrolyzed very slowly or not detectably. The optimum pH for interaction of these isoenzymes with p-nitrophenyl phosphate as substrate ranges from 3.5 to 4.5. L-(+)-Tartrate is a very strong inhibitor, Ki = 0.028 +/- 0.04 mmol/L (mean +/- SE), as are mercuric and fluoride ions in low concentrations. We conclude that type 3 isoenzymes obtained from normal and malignant tissue are very similar, though the malignant tissue appears to have a greater proportion of this type than does normal tissue.