Effects of ethanol and 3,4,-dihydron-2,2-dimethyl-2h-1-benzopyran-6-butyric acid on the solubility of sickle hemoglobin.

The effect of 3,4-dihydro-2,2-dimethyl-2H-1 benzopyran-6-butyric acid (DBA) on the solubility of deoxy-Hb S was evaluated by measuring saturation concentration, c_sat. Plots of c_sat versus DBA concentration in the presence or absence of ethanol gave two parallel lines, indicative of the additive fashion in which ethanol and DBA increase the solubility of deoxy-Hb S. At a $\text{DBA}\text{Hb}$ molar ratio of 10:1, c_sat was increased 16%. Ethanol alone increased c_sat comparably, but at a much higher molar excess (200:1). DBA had no effect on the oxygenation parameters of Hb S. Complementary solubility studies using the salting-out method showed that DBA had no effect on deoxy-Hb S, but decreased the solubility of deoxy-Hb A, oxy-Hb A and oxy-Hb S. Hence, no correlation exists between the effect of DBA on the solubility of deoxy-Hb S measured as c_sat and that measured by the salting-out technique.     

Direct catalytic electrochemistry of sulfite dehydrogenase: Mechanistic insights and contrasts with related Mo enzymes

Under hydrodynamic electrochemical conditions with slow cyclic voltammetry sweep rates we have been able to probe catalytic events at the molybdenum active site of sulfite dehydrogenase (SDH) from Starkeya novella adsorbed on an edge plane graphite electrode within a polylysine film. The electrochemically driven catalytic behaviour of SDH mirrors that seen in solution assays suggesting that the adsorbed enzyme retains its native activity. However, at high sulfite concentrations, the voltammetric waveform transforms from the expected sigmoidal profile to a peak-shaped response, similar to that reported for the molybdenum enzymes DMSO reductase and nitrate reductase (NarGHI and NapAB) where a redox reaction at the active site has been associated with a switch to lower activity at high overpotentials. This is the first time a similar phenomenon has been observed in a Mo-containing oxidase/dehydrogenase, which raises a number of interesting mechanistic problems. The potential at which the activity of SDH becomes attenuated only emerges at saturating substrate conditions and occurs at a potential (ca. + 320mV vs NHE) well removed from any known redox couple in the enzyme. These results cannot be explained by the same mechanism adopted for DMSO reductase and nitrate reductase catalysis.