Hydrophobicity and lectin affinity of alkaline phosphatase isozymes in seminoma and normal testis

Isozymes of alkaline phosphatases (ALP) in seminoma and normal testis were separated by use of high-performance liquid chromatography and a TSK-gel phenyl-5PW column. The tissue-nonspecific (liver) ALP (LAP) was the dominating isozyme, consisting of more than 90% ALP activity. The placental ALP (PLAP)-like enzyme contributed to 4-8% of the total ALP activity. The intestinal isozyme (IAP) could not be identified. The glycosylation patterns of the isozymes were studied using concanavalin A (Con A) affinity chromatography and batch elution with competing sugar. All PLAP activity in placental extracts and LAP activity in liver extracts was bound to Con A-Sepharose. In the tumor extracts, only 50-70% of the PLAP-like enzyme and 20-50% of the LAP activity from seminomas were bound to Con A-Sepharose. A similar binding pattern of the PLAP-like enzyme and LAP was also seen in the normal testes. This variability in Con A reactivity with PLAP or the PLAP-like enzyme was also reflected in serum of seminoma patients and of pregnant women. Thus, ALP expressed in seminoma has different lectin affinity characteristics compared with the same isozyme from placenta and liver, but almost identical to ALP in the normal testes. These findings imply that the PLAP-like enzyme and LAP in the testis can be discriminated from PLAP of placenta and LAP of liver by carbohydrate lectin affinity. It also supports the concept that the increased amounts of ALP in seminomas result from the enhanced eutopic expression of enzymes normally expressed in the testis.