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.
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.