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Levels of Alkaline Phosphatase Isozymes in Human Seminoma Tissue¹

Department of Physiological Chemistry, University of Umeå, S-901 87 Umeå, Sweden [K. H., U. M. D., T. I. S.]; Department of Virology, National Bacteriological Laboratory, S-105 21 Stockholm, Sweden [H. Y., B. E. W.]; Department of Urology, Kanazawa University, Kanazawa, Japan [H. Y.]; and Department of Pathology, South Hospital, Stockholm, Sweden [E. E. B-A.]

The three human isozymes of alkaline phosphatases were quantitatively determined in normal testis and seminoma tissues. The highly selective assays were based on isozyme specific monoclonal antibodies. In the normal testis approximately 90% of the catalytic activity originates from the tissue unspecific alkaline phosphatase, and the remaining activity was due to trace expression of both intestinal (approximately 5%) and placental alkaline phosphatase (PLAP) or PLAP-like isozyme (approximately 5%).

In homogenates of seminoma tissues, highly increased levels of all three isozymes were identified. Both the tissue unspecific alkaline phosphatase and PLAP-like enzymes displayed relative increases of 10- to 100-fold and intestinal alkaline phosphatase 2- to 10-fold compared with normal testis. This finding indicates that the entire genome coding for alkaline phosphatases may be activated in seminomas. The PLAP-like enzyme from seminoma cells comprises a heterogenous population of molecules demonstrating partial heat sensitivity and microheterogeneity upon starch gel electrophoresis in contrast to the pregnancy related PLAP. These findings have implications for the different PLAP assays used in the clinical monitoring of seminoma patients.

¹ The investigation was supported by grants from the Swedish Cancer Society, Lion's Foundation in Umeå, Folksam's research funds, and the Medical Faculty, University of Umeå. A travel grant to K. H. from the Swedish Cancer Society is gratefully acknowledged.

² To whom requests for reprints should be addressed.

Received 11/ 7/86. Revised 2/11/87. Accepted 2/17/87.