Enzymes of Energy‐converting Systems in Individual Mammalian Nerve Cell Bodies1

Abstract— The activities of 7 enzymes (hexokinase, phosphofructokinase, glucose‐6‐P dehydrogenase, 6‐P‐gluconic dehydrogenase, NADP linked isocitric dehydrogenase, malic dehydrogenase and lactic dehydrogenase) were measured in individual nerve cell bodies of 8 different neuronal types: pyramidal cells from cerebral cortex and Amnion's horn, Purkinje cells, giant cells in the reticular formation, Deiters’nucleus cells, facial nucleus cells, anterior horn cells and dorsal root ganglion cells. Samples of similar size were analysed from the molecular layer of cerebellum. The cell bodies were dissected from frozen‐dried tissue sections and weighed on quartz fibre balances. The weights ranged from 0–2 ng for the smallest pyramidal cells to 9 ng for the largest giant cells. The specific enzymatic reactions were carried out in small volumes (0–01–5 μl) under mineral oil (‘oil‐well technique’). The NADPH 2 or NAD formed was amplified by‘enzymatic cycling’and measured fluorometrically. A new cycling method was used for measuring the NAD formed in three of the enzymatic methods. Double cycling was used to measure glucose‐6‐P and 6‐P‐gluconate dehydrogenases in the smallest cell bodies. Each type of neuron exhibited a unique enzyme pattern, but four general patterns could be distinguished. The most variable of the enzymes was glucose‐6‐P dehydrogenase which was nearly 10‐fold higher in anterior horn cells than in pyramidal cells from the cerebral cortex. Malic dehydrogenase was the most constant, with a 3‐fold range from the highest (Purkinje cells) to the lowest (dorsal root ganglion cells).