Binding of Angiotensin I and Angiotensin II to Plasma Proteins Precipitated by Ammonium Sulfate

Abstract

Summary

Angiotensin I and angiotensin II, when added to rat or human plasma, co-precipitate with the later protein fractions, when the plasma is subjected to fractional precipitation by ammonium sulfate. The maximal specific activity of angiotensin II is with the last step (which is mainly albumin) while that of angiotensin I is with an intermediate step. Both angiotensins also coprecipitate with purified albumin when it is precipitated by ammonium sulfate. These results lead us to the conclusion that both angiotensin I and angiotensin II bind to albumin and that angiotensin I also binds to some other protein. We were unable to identify this other protein. Chelating agents, such as EDTA and BAL, do not prevent the binding of either angiotensin to proteins precipitated by ammonium sulfate. Whether a similar binding occurs in vivo still remains unknown.

I thank Miss Carrie Lee for her assistance during the early phases of this investigation.