Activation/inactivation of human angiotensin I converting enzyme following chemical modifications of amino groups near the active site

We have studied the effects of amidination of lysyl residues on the activity of angiotensin I converting enzyme isolated from human kidney. Anion concentration was an important reaction variable. In 4 M chloride or acetate, amidination with methyl acetimidate produced derivatives with up to a 4-fold increase in activity with hippuryl-glycyl-glycine as substrate. Modification with methyl p-hydroxybenzimidate also increased activity while treatment with methyl 4-mercaptobutyrimidate resulted in a 90% loss of activity. The effects of amidination were partially prevented when the reactions were carried out in the presence of the inhibitors, captopril or 5S-benzamido-4-oxo-6-phenyl-hexanoyl-L-proline. These results suggest that lysyl residues are present near the active site while different amino groups have a role in anion activation.