The space structure of a conformationally labile oligopeptide in solution: angiotensin.

The paper describes a new approach to the problem of space structure description for conformationally labile molecules existing in solution as a set of different conformers in dynamic equilibrium. In such a case the "average" model derived exclusively from physico-chemical data represents a virtual structure devoid of physical sense. The proposed approach involves the selection of statistical weights wi for molecular conformers in solution by combined use of spectroscopic data and energy calculations (including the Monte-Carlo technique).

Equilibrium of conformers in solution: spin-labelled angiotensin.

The number of structural parameters were determined for spin-labelled angiotensin in aqueous solution with the use of fluorescence spectroscopy and 1H NMR relaxation induced by the spin label. At the same time all measured parameters were estimated theoretically by means of energy calculations and Monte-Carlo techniques. The matching procedure for experimental and computational data allows one to suggest a dynamic equilibrium between conformers of the molecule in aqueous solution and to estimate the values of their weights.