Protein denaturation in foam - II. Surface activity and conformational change

As part of a study of protein denaturation in foam we have measured the sur face tension and the changes in protein structure occurring at the interfac e for lysozyme, pepsin, BSA, YADH, IgG, and catalase. The apparent CMC valu es were found to be dependent on the size and rigidity of the molecule. The variability of protein damage at a gas-liquid interface in foam was assess ed using these proteins. The foams were produced under controlled condition s in a hubble column and were found to induce conformational changes in the protein molecules, but no fragmentation or disassociation of subunits occu rred. Tertiary structural changes were detected in all the proteins studied , with some proteins forming aggregates. For pepsin, the secondary structur e was also found to be altered. Enzyme solutions were used to determine the degree of biological activity retained after foaming for proteins with dif ferent structural characteristics. The more rigid proteins were found to di splay a low surface activity and a low degree of damage in foam. Pepsin suf fered the highest rate of damage, which is thought to be a result of its in ability to refold following denaturation. (C) 1999 Academic Press.