Interfacial behaviour of wheat puroindolines: monolayers of puroindolines at the air-water interface

Puroindolines are among the major basic and cysteine-rich lipid binding pro teins of wheat seeds. The interfacial properties of puroindoline-a (PIN-a) and puroindoline-b (PIN-b) are important both from a biological and a techn ological point of view. In the work reported here, the interfacial characte ristics of spread monolayers of wheat puroindolines at the air-water interf ace were studied at varying subphase compositions using a Langmuir-Blodgett film balance. The compression isotherms (pi -Asp) were recorded at constan t barrier speed (3.3 cm/min). It was observed that both PIN-a and PIN-b for m stable monolayers at the air-water interface. The stability of the monola yers was found to be dependent on the subphase composition as well as on th e concentration of protein in the spreading solution. When the ionic streng th of the subphase is below 0.50, the compression isotherms of both PIN-a a nd PIN-b remains unaffected with the change in the ionic strength of the su bphase; however. when the ionic strength is above 0.50, the compression iso therms of both PIN-a and PIN-b undergo significant change with an increase in the ionic strength of the subphase. A gradual increase in the values of the collapse pressure (pi (C)) and the limiting area (A(0)) was observed du e to an increase in the ionic strength of the subphase from 0.5 to 4.0, whi ch may be correlated with the salt-induced conformational changes of the pr otein molecule. The presence of NaCl and KCl (ionic strength 1.0) in the su bphase has a comparable effect on the compression isotherms of both PIN-a a nd PIN-b; however, the presence of CaCl2 (ionic strength 1.0) in the subpha se leads to an increase in the values of pi (C) and A(0). A change in the p H of the subphase from 3.0 to 7.2 was to have a significant effect on the v alues of pi (C) and A(0), which may be due to the pH-induced alteration of the protein conformation.