Electrophoretic heterogeneity of alkaline phosphatase isozymes in seminoma and normal testis

Electrophoretic patterns of seminoma- and normal-testis-derived alkaline phosphatase isozymes, the placental alkaline phosphatase (PLAP)-like enzyme and the tissue-nonspecific (liver) alkaline phosphatase (LAP), were studied on starch gel and isoelectric focusing (IEF). Different migration patterns of the PLAP-like enzyme were observed with respect to both seminomas and normal testes on starch gel electrophoresis. On IEF, seminomas showed different staining patterns among different tumors; however, a common main activity was focused at pIs of 4.3-4.6, corresponding to pIs of PLAP. Normal testes showed two enzyme-staining regions, at pIs of 4.1 and 5.0-5.2, which were discriminated from pIs of PLAP and the PLAP-like enzyme in seminoma. The PLAP-like enzyme in seminoma was differentiated from PLAP by digestion with neuraminidase. Neuraminidase treatment simplified the distribution patterns of the PLAP-like enzyme in normal testis, but did not alter the pattern of microheterogeneity in seminoma. Two factors other than sialylation, namely structural modification of the carbohydrate moiety and variation of hydrophobicity, were shown to contribute to the microheterogeneity of the PLAP-like enzyme in seminoma. LAP in seminoma and in normal testis also showed marked electrophoretic heterogeneity and differences in pI distributions from LAP of liver. However, the migration patterns after desialylation were very similar to each other. The findings imply that electrophoretic heterogeneity demonstrated in LAP in seminoma and in normal testis is caused by a difference in sialic acid content in the molecule, and the heterogeneity of the PLAP-like enzyme in seminoma is considerable.