Spectral differences between rhodanese catalytic intermediates unrelated to enzyme conformation.

摘要: Circular dichroism (CD) spectra and UV absorption of two obligatory intermediates in rhodanese catalysis were compared. A broad CD band between 250 287 nm increased a manner stoichiometrically related to the content enzyme-bound persulfide. Titration sample sulfur-substituted (ES) with either cyanide or sulfite gave stoichiometry that is consistent one persulfide/molecule (Mr = 33,000). This result agrees determined by x-ray crystallography method based on quenching intrinsic fluorescence. Cyanolysis persulfide ES accompanied decrease region 300 nm. Cyanide titrations followed change absorbance at 263, 272, 292 expected stoichiometry. The magnitude difference far UV-CD E found here smaller than reported previously. variability suggests differences secondary structure these may not be obligatorily cyanolysis view compatible recent evidence which suggested made different structural relaxation events occur outside catalytic cycle. Furthermore, methods developed will useful studies stability has been central mechanism several enzymes important sulfur metabolism.