Human hexosaminidase isozymes. III. Distribution and activity of isozymes in peripheral blood leukocytes and platelets.

The specific activity and distribution of the isozymes of hex have been studied in platelets, granulocytes, monocytes, and lymphocytes isolated from venous blood. Since there are considerable differences in the content of the various hexosaminidase isozymes in these cell types, the relative activity of the A isozyme, expressed as a percent of total hexosaminidase in a mixed leukocyte preparation, is dependent on the proportion of the individual cell types present in a sample of peripheral blood. Because of variation in the proportion of cell types, the results may not accurately reflect the genotype of the blood donor. In contrast, chromatographic separation and assay of platelet extracts for activity of hexosaminidase isozymes provides a most convenient and satisfactory method of discriminating carriers and noncarriers of the Tay-Sachs mutant gene. Moreover, the ease of isolating platelets and the smaller volume of blood required compared with methods for obtaining purified leukocyte preparations offer additional advantages for identification or verification of the Tay-Sachs heterozygote state.