Angiotensin II was coupled with bovine γ-globulin (BGG) through the following series of reactions.
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By determinations of the aromatic amine and tyrosine contents of p-aminobenzoylangiotensin II, the number of p-aminobenzoyl residues introduced per molecule of angiotensin II was calculated.
Absorption spectra (between 250 and 500 mµ) of BGG complexes of p-aminobenzoylangiotensin II and six different para substituted aromatic amines were compared.
Specific activities (dog units/millimicromole) of the different intermediate products were determined. Presence of a terminal, free amino group does not appear to be an absolute requirement for the biological activity of angiotensin II, since substitution of a p-aminobenzoyl radical in this group yields a product with 40 to 50 per cent of the activity of the parent compound. Angiotensin I, on the other hand, is completely inactivated under identical circumstances. Possible implication of this finding has been discussed.