THE QUANTITATIVE HISTOCHEMISTRY OF ENZYMES OF THE PENTOSE PHOSPHATE PATHWAY IN THE CENTRAL NERVOUS SYSTEM OF THE RAT1

Abstract— Methods are presented for the measurement of the non‐oxidative enzymes of the pentose phosphate pathway in freeze‐dried samples of tissue weighing 2 μg or less. The activities of transketolase (EC 2.2.1.1), transaldolase (EC 2.2.1.2), ribosephosphate isomerase (EC 5.3.1.6), and ribulosephosphate epimerase (EC 5.1.3.1), together with glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49) and 6‐phosphogluconate dehydrogenase (EC 1.1.1.44) have been measured in seven specific regions in the central nervous system of the rat. Michaelis constants and temperature coefficients of these enzymes were obtained on homogenates of whole rat brain. The entire enzymic complement of the pentose phosphate pathway was detected in each of the regions examined. The activities of the non‐oxidative enzymes and 6‐phosphogluconate dehydrogenase did not vary greatly among the different regions examined, whereas the activity of glucose‐6‐phosphate dehydrogenase varied in close correspondence with the lipid content of the various structures. The cellular, granular layer of the cerebellum was exceptional, since it exhibited at least three times more transaldolase activity than that observed in other structures, an observation suggesting an association of transaldolase with nerve cell bodies.