Tyrosine splitting aminopeptidases on cultivated anterior hypophyseal and vascular endothelial cells]

Activities of aminopeptidases for a tyrosine peptide hydrolysis were characterized with Tyrosyl-7-amino-4-methyl-coumarin as substrate on in vitro cultivated anterior pituitary cells, respectively, on aortic endothelial cells. Furthermore the corresponding activities were measured in different fractions of the cells. The activities of the enzymes in soluble fractions of the cell homogenates are comparable with aminopeptidases of cytosolic compartments of other tissue samples. On the other hand remarkable differences exist between Km- and IC50-values of the membrane preparations of both cell types. Furthermore, the substrate degradation on intact cells by provable membrane bound ectoenzymes is identically for both cell types and this degradation is insensitive for amastatin. Our results are discussed with special respect for the importance of the degradation of biological active peptides with N-terminal tyrosine by aminopeptidases on their physiological targets.