H20 splitting step

Similar isotope effects for human isoenzyme I (157c) on kc t and Km for C02 hydration are 1.7. Silverman and Tu (161) report an isotope effect of 2.5 for H2180 release and suggest that the intrinsic isotope effect of intramolecular H+ transfer might be significantly smaller in isoenzyme I than in isoenzyme II. Hence, the H20-splitting step might also limit the rate of C02 hydration in isoenzyme I. Human isoenzyme I has three titratable active-site histidines with pKa values... 

On addition of phenylhydrazine, the polarogram of [Ru" L(H20)] split into three closely separated peaks (Figure 2A.d) with the enhancement of the total diffusion current. The E1/2S of those reduction steps were measured to be -0.155, -0.233 and -0.407 V respectively. The E1/4-E3/4 values of these waves were 30, 55 and 60 mV indicating the first wave was two-electron and remaining two steps were one electron each. The wave analysis data showed the electrode reactions at these potentials were diffusion controlled and reversible. At higher concentrations of phenylhydrazine, there has been no change in peak potentials except the increase of height of the diffusion currents. 

A spectrometric set-up to measure transient spectra in the subpicosecond range is shown in Fig. 12. Half of the amplified pulses from the subpicosecond laser (L) is split into a cell of H20. The residual pulses pass through a variable delay line and are focused to excite the sample (beam 2). The delay is automatically scanned by a stepping-motor-driven stage (M). The emerging continuum beam is split into two parts (beams 0 and 1). Both are focused into the sample (E) and after that on the entrance slit of a spectrograph (S). The resulting two dispersed spectra are recorded by an optical multichannel analyser (D). The description of the passively mode-... 

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