Studies on the structural basis of the heterogeneity of human prostatic and seminal acid phosphatases

We studied possible causes of the electrophoretic heterogeneity of the acid phosphatase (EC 3.1.3.2) purified by affinity chromatography from human prostate and human seminal fluid. The isoelectric focusing pattern in polyacrylamide gel shows numerous bands in the pH range 4.0-5.2 and 5.5-5.9. Treatment with neuraminidase under conditions shown to cause complete removal of sialic acid does not abolish the observed heterogeneity. Although there is a change of the more acidic forms to ones having more basic pI values, at least 4 distinct bands remain. Structural differences at the amino terminal end can be ruled out as the cause of the remaining electrophoretic heterogeneity. Lysine is shown to be the amino terminal amino acid for both the prostatic and seminal fluid enzymes. The sequences of the first 23 amino acids are shown to be identical for the prostatic and seminal fluid acid phosphatases. The functional enzyme contains no metal ion but it can be stoichiometrically inactivated by cupric ion.