Acid phosphatase is a phosphatase, a type of enzyme, used to free attached phosphate groups from other molecules during digestion. It is basically a phosphomonoesterase. It is stored in lysosomes and functions when these fuse with endosomes, which are acidified while they function; therefore, it has an acid pH optimum.
Different forms of acid phosphatase are found in different organs, and their serum levels are used to evaluate the success of the surgical treatment of prostate cancer. In the past, they were also used to diagnose this type of cancer.
Acid phosphatase catalyzes the following reaction at an optimal pH below 7:
Orthophosphoric monoester + H2O → alcohol + H3PO4
Phosphatase enzymes are also used by soil microorganisms to access organically bound phosphate nutrients. An assay on the rates of activity of these enzymes may be used to ascertain biological demand for phosphates in the soil.
Some plant roots, especially cluster roots, exude carboxylates that perform acid phosphatase activity, helping to mobilise phosphorus in nutrient-deficient soils.