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.