EFFECTOR MOLECULES TO PROBE CYTOCHROME-C-OXIDASE ACTIVITY IN GERMINATING PHASEOLUS-VULGARIS L SEEDS

The respiratory effector molecules carbon monoxide (CO), nitrous oxide (N2O), and deuterium oxide (D2O) were used to probe cytochrome c oxid ase (EC 1.9.3.1) activity in mitochondrial particles and enzyme isolat ed from germinating bean seeds. Mitochondrial CO effects were dose-dep endent 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 % N2O. In the presence of 99.8 % D2O, mitochond rial and enzyme activities were 43 % and 52 % of control activities, w ith mitochondrial effects partially reversed in H2O. Visible spectra o f mitochondrial and enzyme preparations showed that CO bound to cytoch rome oxidase at heme a3, while N2O and D2O 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 respirat ion and root length corresponding to reductions in cytochrome oxidase activity. As loss of vigor is the first step in seed deterioration, th ese results would indicate that cytochrome c oxidase activity may be i mportant in the loss of viability.