1991 Volume 20 Issue 3 Pages 125-132
New, Improved isozyme-specific alkaline phosphatase assays were developed. The assays make use of isozyme-specific monoclonal antibodies coated to microtiter plates, and the specific immunoreactivity as well as the catalytic activity of the isozymes are taken into account in the assaying procedure. The new assays require 10-100 fold less monoclonal antibodies than do older ones, and are more rapid and easy to use. The inter- and intra-assay variations were within 10%, and the limits of detection were 0.05IU/l for the placental isozyme, 1IU/l for the intestinal isozyme and 10IU/l for tissue-unspecific isozyme. The activities of the alkaline phosphatase isozymes in sera were determined and recovery rates for the placental and the tissue unspecific isozymes were found to be above 90%, while the recovery rate for the intestinal isozyme differed with respect to type of serum blood group. In sera of blood group type O, the recovery rate was low. Following addition of N-acetylgalactosamine and L-fucose to the assay system, however, the recovery of the intestinal isozyme from sera of blood group type 0 was increased to more than 90%. Normal tissues were tested using the new assays. Relatively high levels of the intestinal phosphatase were found in normal kidney tissue, and normal lung tissue was found to contain significant levels of placental alkaline phosphatase. All tissues investigated were found to contain each of the three alkaline phosphatase isozymes.
