Influence of Several Factors on the Response of Calcitonin Monolayers to Compression at the Air−Water Interface

Abstract

Salmon calcitonin, a polypeptide hormone used in the treatment of osteopathies, formed stable monolayers when spread at the air−water interface from 4:1 (v/v) chloroform/methanol spreading solutions. Monolayers on subphases of pH 2 were more expanded and collapsed at lower surface pressures than those on subphases of pH 6 and 10. Areas and collapse surface pressures decreased with increasing temperature, most markedly at acid pH. Hysteresis was observed when monolayers were repeatedly compressed beyond collapse and decompressed, with compression isotherms shifting to smaller areas in successive cycles. Hysteresis was increased by reducing compression speed and by increasing ionic strength. The results are interpreted as showing that collapse was gradual and partially reversible, consisting in the progressive submersion of the amino acids with the most polar groups (which will have formed a “transition layer” just below the interface) without expulsion of the whole molecule from the film.