The proteins bFGF (basic fibroblast growth factor) and alpha-LA (bovine alpha-lactalbumin) were studied using static and time-resolved fluorescence spectroscopic methods. It was shown that heparin, which activates bFGF, and Suramin, a drug which inhibits bFGF, both bind near the site needed to attach to cells. The fluorescence of alpha-LA is markedly sensitive to metal ion binding, including that of Ca++. This property was used to study binding. The optical properties of alpha-LA were used to measure molecular rotation rates and assess conformational changes. Such fluorescence data gave information not obtainable by other methods. Aspects of the spectral properties of the indole group, which is responsible for the intrinsic fluorescence of proteins containing tryptophan, have been studied. The anomalous lack of proportionality between lifetime g and quantum yield Q has been documented for dipeptides as well as proteins. The origin of this anomaly is complex, and is attributed to different factors, depending on the system. Three factors, viz. static quenching, the presence of conformers, and an apparent change in radiative lifetime, can all increase the g/Q ratio. Calculations of the value of the natural lifetime tau n indicate that in polypeptides, the fluorescence of the indole group arises from a dipole-relaxed state which is different from the initial excited state.
