Distribution of Angiotensin-Converting Enzyme-Like Activity in Vertebrate Tissues

Abstract

Interspecies and interorgan distribution of angiotensin-converting enzyme-like activity (ACELA) was examined in representative species from all vertebrate classes. Activity was determined in tissue homogenates by measuring hydrolysis of the synthetic substrate hippuryl-l-histidyl-l-leucine (HHL). Nearly all animals examined exhibited ACELA in one or more organs, and ACELA was found in at least one species from each class. ACELA was predominant in respiratory (gill and lung), renal, and gastrointestinal tissues. These findings demonstrate that ACELA is (1) phylogenetically old, (2) present in all vertebrate classes, and (3) retained in the same or functionally homologous organs. These results suggest either that ACELA is necessary for the proper physiological function of specific tissues or that the placement of ACELA in strategic vascular locations is of general benefit to the organism. The presence of ACELA in a cyclostome and two elasmobranchs indicates that this enzyme predates the phylogenetic development of the renin-angiotensin system (RAS). Other peptides, possibly kinins, may have been the original substrates of primitive ACE-like enzymes.