Subcellular Distribution of Adenyl Cyclase and Cyclic Phosphodiesterase in Rat Brain Cortex

Abstract

The subcellular distribution of adenyl cyclase and of the cyclic nucleotide phosphodiesterase was studied in fractions and subfractions of the rat brain cortex which had been previously characterized by electron microscopy and several biochemical parameters. Adenyl cyclase was almost wholly particulate, most being found in the mitochondrial fractions with a slightly smaller amount present in the microsomal fractions. The submitochondrial fractions separated by sucrose gradient showed that the specific activity of the adenyl cyclase was low in the myelin and mitochondrial subfractions and high in the three subfractions containing nerve endings. After hyposmotic shock of the mitochondrial fraction, almost all adenyl cyclase remained in particulate subfractions. After gradient separation of the main subfraction, it was found that adenyl cyclase concentrated in two fractions which contain mainly synaptic membranes. Cyclic phosphodiesterase was about 60% particulate although the highest specific activity was found in the soluble fraction. This enzyme was also present primarily in fractions containing nerve endings and not in myelin or mitochondria. After osmotic shock of the primary mitochondrial fraction, half of the enzyme became soluble, but most of the rest remained attached to particulate material. A study of the mitochondrial fraction at several sucrose concentrations suggested that most of the adenyl cyclase in this fraction was compartmentalized.