Cytophotometry of glucose-6-phosphate dehydrogenase activity in individual cells

With the aid of thin films of polyacrylamide gel containing purified glucose-6-phosphate dehydrogenase subjected to cytochemical procedures for the enzyme using tetranitro blue tetrazolium, arbitrary units of integrated absorbance obtained with a Barr & Stroud GN5 cytophotometer were converted into units of enzyme activity. This conversion enabled cytochemical data to be compared directly with biochemical values. The conversion was applied to the cytochemical estimation of glucose-6-phosphate dehydrogenase activity in isolated rat hepatocytes, mouse oocytes, rabbit thymocytes, human granulocytes and human fibroblasts. Several control procedures were performed to confirm the admissibility of this conversion, such as: the estimation of the absorption characteristics of the formazans of tetranitro blue tetrazolium both in solution and precipitated in biological specimens; the linearity of the relationship between the increase of absorbance and incubation time; and the effect of different incubation conditions on the amount of specific formazan production.