Immunochemical quantitation of prostatic phosphatase.

As in most forms of cancer, early diagnosis of prostatic cancer is crucial for a high curability rate. A number of biochemical tests are now available to help identify suspected prostatic cancer in the patient by measuring the activity of acid phosphatase (EC 3.1.3.2) in the patient’s serum. Multiple forms of human acid phosphatase have been described in different organs, but the richest source of this enzyme is the prostate (1_3).1 Acid phosphatase is mainly localized in the lysosomes and is released, when the cell is damaged, into serum and urine. Although various organs possess characteristic patterns of acid phosphatase isoenzymes, as can be seen on zonal electrophoresis, most phosphatases have similar biochemical features, hydrolyzing a wide variety of organic phosphate esters and thus defying differentiation (4). The biochemical tests presently used to measure the activity of phosphatase in serum depend upon the ability of the enzyme to split different substrates at various pH’s. However, this property is not organ-specific, failing to pinpoint the prostatic phosphatase. Thus there has been a problem in interpreting the activities of serum acid phosphatase and the test has not always been reliable in detecting unsuspected cases of prostatic carcinoma (5-8). t Tartrate inhibition of prostatic phosphatase increases the specificity considerably; however, even this method gives a number of false-positive results (8). The renal acid phosphatase shares the property