Prostatic Acid Phosphatase: A Potpourri*

In 1938, Gutman et al. (6) described increased levels of acid phosphatase in metastatic carcinoma of the prostate. Since then, when most of us hear the term "acid phosphatase" we immediately think of prostatic cancer, and justifiably so. The link, however, between the test and the diagnosis is not as clear and simple as many of us would like to believe. I would first like to discuss this enzyme, reviewing some of its chemistry, its clinical value and the pitfalls and problems associated with the routine tests. Then I would like to tell about some work in which we have been involved that we hope will increase the diagnostic value of this enzyme and perhaps point the way to advances in clinical enzymology in other areas. Chemical Assays. First let us remember that the term "acid phosphatase" simply means an enzyme which, at pH below 7 .0, hydrolyzes phosphate esters liberating the phosphate ion and replacing it with an -OH group. Prostatic acid phosphatase is only one of many enzymes in this category. The organic portion of the phosphate ester involved is not specifically defined by the term acid phosphatase, and this brings up our first problem. We do not know the natural physiological substrate of prostatic acid phosphatase. Indeed we know very little about the biological function of this enzyme. Consequently, we must measure its activity using synthetic phosphate esters which are, as far as we know, completely unrelated to prostatic physiology and reproduction. Each new substrate gives rise to a new assay, a new set of units, new degrees of specificity and sensitivity and new problems of interpretation. As previously mentioned, there are many forms