The pH dependence of the conformation of angiotensin peptides by nuclear magnetic resonance: cis-trans isomerism of proline 7.
The pH dependence of the proton NMR spectrum of [Asn1, Val5] angiotensin II in aqueous solution shows the existence of one major and one minor conformation above pH 6.5, the minor conformation representing 12 +/- 2% of the total peptide. A similar observation has been made for (Asn1, Val5) angiotensin I and Val-Tyr-Val-His-Pro-Phe. This effect is not due to the presence of angiotensin-like impurities in the peptide samples. We have shown two expected impurities, [beta-Asp1, Val5] angiotensin II and [Asn1, 3-Bzl-Ty4, Val5] - angiotensin II, to be absent, and a third impurity [Asn1, Val5, D-His6] angiostensin II, to be present at less than or equal to 2.1 mol%, too little to account for the observed amount (12 +/- 2%) of minor conformation. The carbon-13 spectrum of the hexapeptide at high pH shows that the major conformation has Pro7 in the trans form and the minor conformation has Pro7 in the cis form.
D000595:Amino Acid Sequence; D000804:Angiotensin II / Q000031:analogs & derivatives; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D010446:Peptide Fragments / Q000032:analysis; D011392:Proline / Q000032:analysis; D011487:Protein Conformation; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D010446:Peptide Fragments; D000804:Angiotensin II; D011392:Proline