1. Enzymes of normal and leukemic glass column separated leukocytes were assayed with fluorometric (glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, lactic dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase and isocitric dehydrogenase) and radioisotope (DNA polymerase) micromethods.

2. Most results were obtained by direct assay of the specific cell type. Some required simple calculation. It was demonstrated that the enzyme activity of mixed cell suspensions was the sum of the enzyme content of the component cells, at least for the enzymes studied.

3. Assays of mixed cell suspensions may give an erroneous picture. Thus changes in differential cell counts, as well as alterations in enzyme content of individual cells, must be taken into account for correct interpretation.

4. Changes in enzyme content of mixed cell suspensions after therapy were due chiefly to alterations in the differential cell count rather than to changes in the enzyme content of individual cell types.

5. The patterns of assays of the carbohydrate metabolizing enzymes studied, except isocitric dehydrogenase, paralleled each other. Highest values were found in mature PMN leukocytes and lowest in blasts. With isocitric dehydrogenase absolute values were much lower, while the highest assays were found in myelocytes.

6. DNA polymerase content correlated well with the ability of a cell to divide. It was highest in blasts and lowest in mature PMN leukocytes.

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