Evidence for dynamically determined conformational states in rhodanese catalysis.

Physical and kinetic studies have been used to explore hysteretic effects that are observed in rhodanese catalysis at pH 5 and also at neutral pH when the ionic strength of the medium is high. Experiments that involve observation of changes in intrinsic protein fluorescence of the enzyme and kinetic investigation of its interactions with product thiocyanate anion at pH 5 have implicated enzyme isomerization as the cause of hysteresis. Taken all together, the data indicate that the conformations of enzyme forms in the catalytic cycle are dynamically determined, depending on the relative rates of conformational relaxation and catalysis as influenced by the concentrations of substrates and products.