The intracellular distribution of glycolytic and other enzymes in rat-brain homogenates and mitochondrial preparations

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Abstract
Homogenates of rat brain have been fractionated by centrifuging on 0-3[image]-sucrose, and mitochondrial preparations have been subfractionated in dense media. Part (15%) of the hexokinase could not be sedimented, but 75% was present in the mitochondrial fractions and could not be separated from succinic dehydrogenase. The hexokinase in the mitochondrial fraction was not liberated by freezing and thawing. Each of the other glycolytic enzymes was present mainly (70-90%) in the clear cytoplasmic fraction. Only traces of DPN-dependent [alpha]-glycerophosphate dehydrogenase could be detected in brain homogenates. The particulate portions having lacticdehydrogenase and phospho-fructokinase activity were mainly associated with the mitochondrial fraction. Substantial separation of the cholinesterase, esterase and lactic dehydrogenase from the succinic dehydrogenase and hexokinase of brain-mitochondrial preparations was achieved a light fraction containing 70-80% of the former three enzymes and a heavy fraction containing 70-80% of the latter two enzymes could be obtained. A slight separation of cholinesterase and esterase was achieved by a double subfractionation of brain particles.