Orientation, accessibility, and mobility of equilenin bound to the active site of steroid isomerase
- 25 July 1989
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 28 (15), 6269-6275
- https://doi.org/10.1021/bi00441a019
Abstract
The fluorescent aromatic steroid equilenin, which contains a .beta.-naphthol moiety, is bound by 3-oxo-.DELTA.5-steroid isomerase. The excitation and emission fluorescence spectra of equilenin when bound to the enzyme, as well as the fluorescence decay time, are indicative of ground-state ionization. In view of the high efficiency of tyrosine quenching, which approaches 100%, the .beta.-naphthol moiety of equilenin must be in proximity to all three tyrosines of steroid isomerase to account for the observed efficiency of radiationless energy transfer. From the observed response to an external quencher, it appears that enzyme-bound equilenin is largely shielded from solvent. Fluorescence anisotropy measurements indicate a high degree of immobilization of the bound ligand. These models are consistent with proposed models of the enzyme-substrate complex.This publication has 2 references indexed in Scilit:
- A reinvestigation of the mechanism of Pseudomonas testosteroni .DELTA.5-3-ketosteroid isomeraseJournal of the American Chemical Society, 1981
- A novel chemical modification of delta 5-3-ketosteroid isomerase occurring during its 3-oxo-4-estren-17 beta-yl acetate-dependent photoinactivation.Journal of Biological Chemistry, 1977