Aspects of protein reaction dynamics: Deviations from simple behavior

Proteins are complex systems so that their reactions may have characteristi cs not often observed in small molecules. Two common aspects of small molec ule reactions are an exponential time dependence and Arrhenius-like tempera ture dependence. This review shows that corresponding behavior is not alway s observed in reactions involving proteins. Bond-making and bond-breaking r eactions, as well as conformational changes, which do not involve chemical bonds, are discussed. As examples of bond making, bond breaking reactions, enzyme catalysis by triosephosphate isomerase and ligand binding by myoglob in are considered. Several reactions involving conformational changes are d escribed. They include aromatic side chain rotations, loop/lid opening and closing motions, quaternary structural changes in hemoglobin, and protein f olding. In some of these cases, deviations from simple small molecule behav ior have been observed, but it is evident that more information is needed f or a complete understanding. The protein folding reaction, which is most co mplex because it involves the entire polypeptide chain, is analyzed in some detail.