What is Acid Phosphatase?

Acid phosphatase (ACP) is a type of enzyme manufactured by the body. Like all enzymes, it is composed of specialized proteins that catalyze, or stimulate, certain biological reactions. ACP is classified as a hydrolase enzyme because its purpose is to catalyze the hydrolysis of a chemical bond. Specifically, it targets and breaks the molecular bonds of phosphate groups.

There are several different types of this enzyme that exhibit different characteristics and behaviors. For example, like many other types of phosphatases, tartrate acid phosphatase is exclusive to mammals, but differs by being resistant to the inhibitory effects of L (+) tartrate. Some members of this family are classified as human genes, such as ACP-1 and lysophosphatidic acid, also known as ACP-6.

Generally speaking, ACP can be found in certain organs and tissues, including blood cells, bone marrow, the spleen, pancreas, liver, and kidneys. This substance is found in the greatest concentration in the prostate, however, and up to 1,000 times greater in seminal fluid than any other bodily fluid. The latter fact is useful in the science of forensics since the detection of prostatic acid phosphatase (PAP) in vaginal tissue measuring levels greater than 3 U/ML (units per milliliter) is used as supporting evidence that a rape has occurred. Additional evidence to confirm that the presence of this enzyme is from semen rather than vaginal fluid is gathered from a PAP assay, which is a quantitative measurement of the various isoenzymes found in ACP generated exclusively by the prostate. In addition, the administration of this test typically coincides with a prostate-specific antigen (PSA) test, which confirms the presence of sperm.

Measuring serum levels of ACP is useful in the diagnosis of a variety of medical conditions. For example, abnormal levels may indicate the presence of systemic infection, anemia, hepatisis, thrombophlebitis, or hyperparathyroidism. Elevated levels of PAP in particular is associated with inflammation of the prostate, as well as prostate cancer that has metastasized to the bone. Phosphatase testing is also used to assess enzymatic damage caused by kidney disease, liver disease, or a heart attack. This test is also performed when certain chronic metabolic or bone diseases are suspected, such as Gaucher disease and Paget disease.

A simple blood test can be used to determine the levels of this enzyme. The blood sample is exposed to one of several agents to elicit an enzymatic reaction, namely 4-aminoantipyrine, or a solution of disodium phenyl phosphate and citrate. To measure levels of PAP, tartrate is used. By observing the reaction with these different agents, the clinician is able to determine which tissue is releasing phosphatase enzymes into the bloodstream and what type they are. Usually, the test results are available within one to two days.