Comparison of soluble aminopeptidases in human cerebral cortex, skeletal muscle and kidney tissues

In an attempt to elucidate the cellular function of the soluble aminopeptidases (with which the majority of tissue aminopeptidase activity is usually associated) we have determined the distribution and characteristics of these enzymes in three functionally dissimilar human tissues (cerebral cortex, skeletal muscle and kidney cortex), using a systematic experimental approach. Following fractionation of brain, muscle or kidney soluble extracts via anion exchange chromatography, four aminopeptidase enzymes types (alanyl-, arginyl-, leucyl- and pyroglutamyl-) were identified; the absolute and relative activities for corresponding enzymes were similar in each tissue. Following further purification of each enzyme type from each tissue (via liquid chromatography/preparative electrophoresis), corresponding enzyme types were found to have similar characteristics (pH optimum of activity, action of enzyme effectors, substrate specificity and molecular mass). Since the same enzymes, with correspondingly similar distribution and characteristics are present in such functionally dissimilar tissues, it is suggested that the principal role for the soluble aminopeptidases (in contrast to the membrane-associated enzymes, which may function in the catabolism of neuropeptides) is in the final stages of the general intracellular protein catabolism cascade, via hydrolysis of oligopeptide intermediates to free amino acids.