Structural organization of membrane and soluble forms of somatic angiotensin-converting enzyme

The catalytic activity and quaternary structure of soluble (s) and membrane (m) forms of angiotensin-converting enzyme (ACE) were studied in reversed micelles of ternary system Aerosol OT-water-octane. The profile of the depe ndence of the catalytic activity of the two enzyme forms on the degree of s urfactant hydration (micellar size) had several optima corresponding to the function of various active oligomeric enzyme forms; the curves for the s- and m-forms of ACE were different. Data of sedimentation analysis prove tha t in reversed micelles, s-ACE can exist as monomers, dimers, or tetramers d epending on the hydration degree, and the m-form is present as dimers and t etramers only. The values of the kinetic parameters for the hydrolysis of t he substrate furylacryloyl-Phe-Gly-Gly by all the enzyme forms were determi ned, and the data indicate that the activity of the m-form is enhanced by o ligomerization. The ACE activity strongly depends on the medium; it is high er when ACE is in contact with matrix or other enzyme molecules.