INFLUENCE OF SEVERAL FACTORS ON THE RESPONSE OF CALCITONIN MONOLAYERSTO COMPRESSION AT THE AIR-WATER-INTERFACE

Salmon calcitonin, a polypeptide hormone used in the treatment of oste opathies, formed stable monolayers when spread at the air-water interf ace from 4:1 (v/v) chloroform/methanol spreading solutions. Monolayers on subphases of pH 2 were more expanded and collapsed at lower surfac e pressures than those on subphases of pH 6 and 10. Areas and collapse surface pressures decreased with increasing temperature, most markedl y at acid pH. Hysteresis was observed when monolayers were repeatedly compressed beyond collapse and decompressed, with compression isotherm s shifting to smaller areas in successive cycles. Hysteresis was incre ased by reducing compression speed and by increasing ionic strength. T he results are interpreted as showing that collapse was gradual and pa rtially reversible, consisting in the progressive submersion of the am ino acids with the most polar groups (which will have formed a ''trans ition layer'' just below the interface) without expulsion of the whole molecule from the film.