Subcellular distribution of enkephalin-dipeptidyl carboxypeptidase (enkephalinase) in rat brain

Abstract

The distribution of enkephalinase activity i.e. of the peptidase activity cleaving the Gly 3-Phe 4 bond of enkephalins, has been established in subcellular fractions of rat cerebral cortex and striatum and compared with that of opiate receptors labelled with [ 3H] dAla 2-Met-enkephalinamide. The fractions were obtained by differential and density gradient centrifugations and their purity assessed by measuring levels of a series of biochemical markers. A major part of enkephalinase activity is associated with the P 2 fraction containing isolated nerve-endings and the subfractions of lysed P 2 containing synaptosomal membranes display the highest enrichment. Another important part of enkephalinase activity is associated with the microsomal P 3 fraction, whereas the enzyme activity is hardly detectable in cytoplasm or synaptic vesicle fractions. The distribution of enkephalinase activity between the various fractions and subfractions strikingly parallels that of enkephalin receptors. These data support the hypothesis that enkephalinase is selectively located in neuronal membranes in the vicinity of enkephalin receptors, as suggested by previous regional distribution and lesion studies, and that it might be responsible for the inactivation of endogenous enkephalins.