The simultaneous determination of carbon dioxide release and oxygen uptake in suspensions of plant leaf mitochondria oxidizing glycine.

The construction and operation of a device for continuous measurement of CO(2) release by suspensions of respiring mitochondria is described. A combination of this device with a Clark-type O(2) electrode was used for simultaneous measurement of respiration and of CO(2) release by spinach and pea leaf mitochondria with glycine as substrate. Both mitochondrial preparations showed high rates of respiration and high respiratory control ratios. The addition of oxaloacetate not only inhibited O(2) uptake substantially, but also greatly stimulated glycine oxidation as monitored by CO(2) release. In spinach leaf mitochondria, the maximal rates of glycine oxidation thus obtained, were two times higher than the rate of glycine oxidation required at average rates of photorespiration. It is concluded from these results that under saturating conditions the capacity of glycine oxidation by intact mitochondria exceeds the capacity of glycine-dependent respiration.