The localization of cerebral phosphoprotein phosphatase

Abstract

The distribution of phosphoprotein phosphatase in various regions of ox brain has been measured. Activity was high in the pariental and cerebellar cortex and in the caudate nucleus, low in the corpus callsoum, the floor of the IVth ventricle and the medulla, and intermediate in the thalamus, putamen and globus pallidus. This distribution has been compared with that found by other authors for a variety of cerebral enzymes. The subcellular localization of phosphoprotein phosphatase in guinea-pig cortex and whole brain has been examined. The enzyme showed a bimodal distribution, 56-60% of the activity being present in the soluble supernatant and 20-30% in the mitochondrial fraction. The activity present in the nuclear fraction (10%) could be separated from the nuclei by density-gradient centrifuging and concentrated in a mitochondria-rich subfraction. Small amounts of activity in the light -mitochondrial and microsomal fractions were attributed to contamination with mitochondria or with supernatant. No separation of phos-phoprotein-phosphatase and succinate-dehydrogenase activities within the mitochondrial fraction was obtained by density-gradient centrifuging. The similarity of distribution of phosphatase and of phosphoprotein suggests a close relationship of enzyme and substrate in vivo.