Antigenic and molecular relationship of human prostatic acid phosphatase isoenzymes

Human prostate contains two major acid phosphatase isoenzymes, 2 and 4. Isoenzyme 2 is a glycoprotein with slow electrophoretic mobility. Treatment with sialidase increases its electrophoretic mobility to approach that of isoenzyme 4 which contains no carbohydrate. The identical protein structure of isoenzyme 2 and 4 was revealed by their antigenic identity. Serum acid phosphatase isoenzyme 5 is a different protein species and has no antigenic relationship to isoenzymes 2 and 4. Our results indicate that the elevation of isoenzyme 5 in late stages of prostatic carcinoma with bone metastases is attributable to increased osteoclastic activity.