Abstract
The hydroly-sis of aromatic esters by human serum was studied. Two aryl-esterases were obtained by electrophoresis: An arylesterase I (migrated with prealbumin and albumin; stable to phosphoric esters, especially E 605), and an arylesterase II (migrated between albumin and [alpha]1; sensitive to phosphoric esters). Substrate specificity, reaction kinetics and the action of some inhibitors were studied. Under the given conditions, serum cholinesterase has practically no action on [beta]-naphthylpropionate.