Effector Molecules to Probe Cytochrome c Oxidase Activity in Germinating Phaseolus vulgar/s L. Seeds

The respiratory effector molecules carbon monoxide (CO), nitrous oxide (N 20), and deuterium oxide (D20) 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% N20. In the presence of 99.8 % D20, mitochondrial and enzyme activities were 43 % and 52 % of control activities, with mitochondrial effects partially reversed in H 2O. Visible spectra of mitochondrial and enzyme preparations showed that CO bound to cytochrome oxidase at heme a 3 , while N20 and D20 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.