Oxidative Phosphorylation Ability of Mitochondria frqm Barley Seedlings in Heavy Water (D₂O)

Oxidative phosphorylation ability of mitochondria from barley seedlings raised in H₂O and 50% D₂O has been examined polarographically. Oxygen uptake was inhibited by D₂O and ADP: O ratios were observed to be higher than in H₂O. Phosphorylation efficiency, as Pi esterified, measured by colorimetric and isotopic methods showed no difference in values between control and treated plant mitochondria ATP ase and SDH activities were lowered by D₂O and so also the substrate oxidation in uncoupled mitochondria. These results suggest that reactions involving either removal or addition of hydrogen may be the rate limiting steps due to replacement of D for H.