Glucose-6-phosphate dehydrogenase is enriched in oligodendrocytes of the rat spinal cord. Enzyme histochemical and immunocytochemical studies.

Glucose-6-phosphate dehydrogenase (G6PD) was localized in rat spinal cord by catalytic enzyme histochemistry and immunocytochemistry. G6PD detected by either method was shown to be strongly enriched in cell bodies and processes of oligodendrocytes, whereas in the compact myelin G6PD was not detected. The enzyme histochemical procedure for the demonstration of G6PD was also adapted for microphotometric measurements of G6PD activity in the spinal cord white matter. There was a linear relationship between G6PD activity and section thickness up to 14 microns and between G6PD activity and reaction time up to 5-6 min as demonstrated by kinetic and end-point measurements. Significantly lower activities were measured in end-point measurements than in kinetic measurements because of formazan loss during rinsing. Methoxyphenazine methosulphate as an exogenous electron carrier and sodium azide as a blocker of the respiratory chain significantly increased the demonstrable G6PD activity. The Km was 0.62 mM and the Vmax 3 mumol glucose-6-phosphate/cm3 wet tissue and per min at 25 degrees C. It is concluded that G6PD in oligodendrocytes may be important for the generation of NADPH required for lipid biosynthesis related to myelogenesis, and reduction of glutathione required for protection of membrane sulphydryl groups.