Isoenzymes of alkaline phosphatase in germinoma cells

Utilizing 18 germinomas, the characteristics of isoenzymes of alkaline phosphatase (ALP) in germinoma cells were examined by light and electron microscopic enzymohistochemical and immunohistochemical techniques and biochemical methods including inhibition tests, electrophoresis and electrosyneresis. ALP in germinoma cells was generally located on the cell surface. In a few germinoma cells, however, ALP was seen not only on the cell membrane but also in the endoplasmic reticulum. Enzymohistochemically as well as biochemically, ALP in germinoma cells was little sensitive to L-phenylalanine, moderately sensitive to L-homoarginine and somewhat resistant to heat in its inhibition tests. Immunohistochemical examinations and electrosyneresis showed the presence of the placental type of ALP in germinoma cells and biochemical analyses revealed that the heat-stable component of ALP in germinoma cells was consistent with the D-variant of the placental type of ALP. Therefore, germinoma cells possessed mixed isoenzymes of ALP, consisting mainly of the liver/bone type and a small amount of D-variant of the placental type on the cell surface. The prominent expression of ALP in germinoma cells may be due to the enhanced expression of gonadal genes active in the germinoma genome.