Binding of renin and angiotensinogen to macromolecules in plasma studied by sedimentation equilibrium centrifugation

Plasma from normal and aggressive mice was subjected to sedimentation equilibrium centrifugation in an air-driven centrifuge. The aim was to study the apparent molecular weight of renin and angiotensinogen in undiluted plasma. Both renin and angiotensinogen appeared heterogeneous with respect to molecular size, suggesting binding to plasma macromolecules. Subsequent high pressure liquid chromatography, using a size exclusion column, demonstrated molecular homogeneity and molecular weights as found in noncentrifuged plasma, indicating that the binding is easily reversible. It is concluded that renin and angiotensinogen in undiluted and unfractionated plasma are weakly bound to plasma macromolecules. This may reduce their activity and to some extent explain the previously observed apparent inhibition of the enzymatic activity.