REDISTRIBUTION OF RAT BRAIN ESTERASES DURING SUBCELLULAR FRACTIONATION

Carboxylic ester hydrolases (nonspecific esterases) and acetylcholinesterase were determined in particulate fractions of rat cerebrum after differential and density-gradient centrifugation. The crude mitochondrial fraction was osmotically shocked by distilled water. When related to the total activity of the original homogenate, 12% of nonspecific esterases and 18.5% of acetylcholinesterase were recovered in the crude mitochondrial fraction. Assays of mitochondrial subfractions showed that 68 and 63.8% of these enzyme activities respectively were recovered in the myelin. The high activity of the myelin subfraction appeared to be due to artifactual redistribution of enzyme. The amount of enzyme released and subsequently bound to subcellular membranes during preparative manipulations might depend on protein-lipid interactions. The synaptic membrane subfraction retained by 0.9 M sucrose differed from the other subfractions in the degree of retention of membrane-bound enzymes during suspension in media of varying pH, osmolality and ionic concentration. These membranes may have a special and physiologically significant molecular organization which differs from that of other membrane fractions. © 1969.