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Presence of the Rare D-Variant Heat-stable, Placental-type Alkaline Phosphatase in Normal Human Testis¹

La Jolla Cancer Research Foundation, La Jolla, California 92038 [W. H. F.], and the Tufts Cancer Research Center and the Department of Pathology, Tufts University School of Medicine, Boston, Massachusetts 02115 [C. H. C., D. A., W. H. F.]

In 11 adult testes studied, about 0.3 to 4.6% of the total alkaline phosphatase activity was heat stable and L-phenylalanine sensitive but L-homoarginine insensitive. The testicular heat-stable enzyme was more susceptible to inhibition by L-leucine and ethylenediaminetetraacetate than were the normal placental and intestinal enzymes.

By antibody-directed enzyme inhibition test, the testicular heat-stable enzyme cross-reacted completely with normal placental enzyme but clearly distinguished itself from a heat-stable component of normal intestinal enzyme. Thus, placental alkaline phosphatase D-variant is synthesized in testis, indicating that the gene for elaborating this placental protein is probably already active in the testicular cells. The high incidence of this protein in cancers of testis and ovary is probably due to its increased production by gonadal genes present in the genome of these particular tumors.

¹ Aided in part by Grants-in-aid CA 12924 and CA 21967-01 of the National Cancer Institute, NIH, Bethesda, Md., and by Grant 935-M of the Council for Tobacco Research, New York, N. Y.

² Present address: Syva Research Institute, Palo Alto, Calif. 94303.

³ Present address: Dartmouth Medical School, Hanover, Mass. 02339.

⁴ To whom requests for reprints should be addressed, at La Jolla Cancer Research Foundation, P. O. Box 1376, La Jolla, Calif. 92037.

Received 4/21/78. Accepted 2/ 7/80.

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