Fluorescence studies of bilayers and proteins: Critical behavior and genetic engineering

Fluorescence decay and anisotropy studies of parinaric acid in phospholipid bilayers have demonstrated the presence of density fluctuations exhibiting critical behavior in these nominally single phase structures. The anisotropy behavior is used to extract the second and fourth rank order parameters <P2> and <P4> for comparison with models of acyl chain order. A recent study of parinaric acid in hexagonal urea inclusion complexes has demonstrated that the strongly allowed transition is polarized at an angle with respect to the chain axis. The implications of this for the interpretation of anisotropy experiments is discussed. The lysozyme from bacteriophage aq has been engineered in modified forms containing only one tryptophan residue and with substitutions near the buried tryptophan residue 138. Simple changes in the structure appear to result in large changes in the dynamics of this residue. These observations are compared with the results of molecular dynamics computations.