Eric E. Roos

The anesthetic nitrous oxide affects dioxygen utilization by bovine heart and bean seed mitochondrial particles

Nitrous oxide affects dioxygen utilization by both bean seed and bovine heart submitochondrial particles when either succinate or reduced cytochrome c are used as substrates. Bovine heart particles exhibit reversible, dose-dependent partial inhibition of respiratory activity when exposed to N2O. Bean seed particle respiration is stimulated by low levels of N2O, but higher concentrations are inhibitory. These findings can be explained in terms of one locus of anesthetic action: cytochrome c oxidase, the terminal component of the mitochondrial respiratory chain. Alterations in respiration rates are expected to make important contributions to anesthesia in animals and to control of germination in plants.

Effector molecules to probe cytochrome c oxidase activity in germinating Phaseolus vulgaris L. seeds

Summary The respiratory effector molecules carbon monoxide (CO), nitrous oxide (N 2 O), and deuterium oxide (D 2 O) were used to probe cytochrome c oxidase (EC 1.9.3.1) activity in mitochondrial particles and enzyme isolated from germinating bean seeds. Mitochondrial CO effects were dose-dependent and readily reversible, with maximal activity inhibition of 58 % and 81 % for mitochondria and oxidase, respectively, in the presence of 80 % CO. Cytochrome oxidase activity was reversibly inhibited 36 % in the presence of 80 % N 2 O. In the presence of 99.8 % D 2 O, mitochondrial and enzyme activities were 43 % and 52 % of control activities, with mitochondrial effects partially reversed in H 2 O. Visible spectra of mitochondrial and enzyme preparations showed that CO bound to cytochrome oxidase at heme a 3 , while N 2 O and D 2 O did not directly affect the ligand binding site. Seed germination was not changed in the presence of these molecules, but reductions were observed in seedling respiration and root length corresponding to reductions in cytochrome oxidase activity. As loss of vigor is the first step in seed deterioration, these results would indicate that cytochrome c oxidase activity may be important in the loss of viability.