On the effect of sodium dodecyl sulfate on the structure of beta-galactosidase from Escherichia coli. A fluorescence study

An understanding of the structure-function relationship of proteins under d ifferent chemical-physical conditions is of fundamental importance for an u nderstanding of their structure and function in cells. In this paper we rep ort the effects of sodium dodecyl sulfate and temperature on the structure of P-galactosidase from Escherichia coli, as monitored by fluorescence spec troscopy. The structure of the protein was studied in the temperature range of 10-60 degreesC in the absence and presence of sodium dodecyl sulfate by frequency-domain measurement of the intrinsic fluorescence intensity and a nisotropy decays, The time-resolved fluorescence data in the absence of SDS indicated that at 10 degreesC the tryptophanyl emission decays were well d escribed by a three exponential decays model, and that the temperature incr ease resulted in shortening of the long-lived component with little change in the short- and middle-lived components. The addition of SDS to the prote in solution also affected the long-lived component. The effects of the dete rgent and temperature on the enzyme structure were also investigated by mea ns of quenching experiments and anisotropy decays, The obtained results sho wed that the presence of SDS confers more flexibility to the protein struct ure, and suggest a strict relation between enzyme activity and protein flex ibility.