Purification and characterization of ovine angiotensinogen.

The two major forms of ovine angiotensinogen (renin substrate) have been purified to homogeneity from plasma and a third form has been partially purified. The purification procedure involved ammonium sulphate fractionation, gel filtration, ion-exchange chromatography and chromatofocusing. The pure proteins have apparent relative molecular masses of 56 000 as determined by sodium dodecyl sulphate gel electrophoresis. The amino acid compositions of the two major forms appear to be the same; however, they do have different carbohydrate compositions. Antibodies raised against the a form showed complete cross-reactivity with the b and c forms. Both major forms have the same amino-terminal sequence, which includes that of ovine angiotensin I: Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu. Thus ovine angiotensin is the Ile5 form and not the Val5 form as had previously been suggested.