In an attempt to elucidate the cellular function of the soluble aminopeptidases, we have analysed their activity in several subcellular fractions (synaptosomal, mitochondrial, microsomal, nuclear and cytosolic fraction) and in different areas (amygdala, hypothalamus, hippocampus, striatum, frontal cortex, occipital cortex and parietal cortex) of the human and the rat brain. The enzymes assayed in this study were five cytosolic aminopeptidases identified inmammalian brain tissues: alanyl-aminopeptidase, arginyl-aminopeptidase, leucyl-aminopeptidase, pyroglutamyl-peptidase I and aspartyl-aminopeptidase. The regional comparative study revealed significantly higher activities of alanyl-aminopeptidase activity in the human brain, with arginyl-aminopeptidase activities being higher in the rat brain. In the subcellular study, while the alanyl- and arginyl-aminopeptidase activities were quite homogeneous in all the subcellular fractions, the leucyl-aminopeptidase, pyroglutamyl-peptidase I and aspartyl-aminopeptidase activities were significantly higher in the synaptosomal fraction. The differential distribution of these enzymes could suggest that these activities have different functions in the distinct subcellular structures of the human and the rat brain.
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