COMPARISON OF INACTIVATION AND CONFORMATIONAL CHANGES OF YEAST D-GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE DURING DENATURATION BY GUANIDINIUM CHLORIDE
3-磷酸甘油醛脱氢酶胍变性时的活力及构象变化

Changes in intrinsic protein fluorescence of yeast GAPDH have been compared with its inactivation during denaturation in GuHCI solutions. The holo-and the apo-enzymes are completely inactivated at GuHCI concentrations less than 0.5M and this is accompanied by marked decrease in flurescence emission intensity and red Shift of the emission maxima at 335 nm suggesting exposure of aromatic residues. It has been reported before that during the denaturation of the muscle enzyme, following an initial decrease, there is a region of relatvely little fluorescence changes between 0.4-1.2 M GuHCI.For the yeast enzyme, the decrease in emission intensity is continuous with the increase in GuHCI concentration. At 0.7M GuHCI, the fluorescence change is monophasec with a first order rate constant of 1.3×10-4S-1 but the inactivation is a biphasic process with a fast phase rate constant greater than 0.1×S-1. This is 3 order of magnitudes faster than the corresponding unfolding rate. The slow phase inactivation rate, first order constant of 2.1×10-4 S-1 , is close to that of the unfolding rate as measured by fluorescence changes.