Alkaline phosphatase of mouse teratoma stem cells: immunochemical and structural evidence for its identity as a somatic gene product

Abstract

The immunochemical and structural characteristics of the alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] from mouse teratoma stem cells derived from the OTT-6050 teratoma (ascitic and solid tumors and the F9 and PCC4 cell lines) have been compared to those of the alkaline phosphatases expressed in normal mouse placenta and several adult organs. Crossreactivity of the stem cell alkaline phosphatase with antisera reacting with placental, kidney, liver, and brain alkaline phosphatases indicated that the stem cell enzyme had common antigenic determinants. Structural studies utilizing two-dimensional electrophoresis of the (32)P-labeled alkaline phosphatase subunits showed that the stem cell, placental, and kidney alkaline phosphatases differed only in their sialic acid content and comigrated after removal of terminal sialic acid by neuraminidase digestion. Furthermore, one-dimensional peptide mapping of partial proteolysis fragments from (32)P-labeled enzymes demonstrated identical fragmentation patterns for the stem cell and somatic enzymes. These immunochemical and structural data indicate that the stem cell alkaline phosphatase is the same core enzyme as that produced in the mouse placenta and kidney, with different amounts of terminal sialic acid. The one mouse alkaline phosphatase examined that differed from the other enzymes was the intestinal alkaline phosphatase. This isoenzyme was not immunochemically crossreactive with the other alkaline phosphatases, did not comigrate in two-dimensional electrophoresis after neuraminidase digestion, and did not give identical peptide maps after partial proteolysis.