The effect of deuterium oxide on respiratory-chain phosphorylation in sub-mitochondrial particles

The effect of pH and ionic strength on the pre-steady-state reaction of cytochrome c and cytochrome aa3

(1) In the pH range between 5.0 and 8.0, the rate constants for the reaction of ferrocytochrome c with both the high- and low-affinity sites on the cytochrome aa3 increased by a factor of approx. 2 per pH unit. (2) The pre-steady-state reaction between ferrocytochrome c and cytochrome aa3 did nt cause a change in the pH of an unbuffered medium. Furthermore, it was found that this reaction and the steady-state reaction are equally fast in H2O and 2H2O. From these results it was concluded that no protons are directly involved in a rate-determining reaction step. (3) Arrhenius plots show that the reaction between ferrocytochrome c and cytochrome aa3 requires a higher enthalpy of activation at temperatures below 20 degrees C (15--16 kcal/mol) as compared to that at higher temperature (9 kcal/mol). We found no effect of ionic strength on the activation enthalpy of the pre-steady-state reaction, nor on that of the steady-state reaction. This suggests that ionic strength does not change the character of these reactions, but merely affects the electrostatic interaction between both cytochromes.

Inhibitory effect of deuterium oxide on glucose oxidation by pancreatic islets

The inhibition of insulin release by deuterium oxide has been interpreted by its stabilizing action on the microtubular system of the beta-cell. Because only indirect information exists about beta-cell metabolism in the presence of D2O, the effect of D2O (99.7%) on glucose oxidation by pancreatic islets was studied. Heavy water reduced 14CO2 formation from [U-14C]glucose (16.7 mM) by ob/ob mouse and rat islets by 50 and 30%, resp. Omission of calcium from H2O-containing media resulted in a 40% diminished glucose oxidation by ob/ob mouse islets. In the absence of calcium, D2O led to a further decrease in 14CO2 production (60%). Erythrocytes oxidized similar amounts of glucose in the absence and presence of D2O. Effects of D2O on glucose transport and mitochondrial respiration are discussed as possible causes of the decreased 14CO2 formation in islet tissue. It is concluded that the inhibition of insulin release by D2O need not necessarily be ascribed to its stabilizing effect on microtubules, but may also be due--at least in part--to the reduction of islet glucose oxidation.