Generation of O2- and tyrosine cation-mediated chemiluminescence during the fertilization of sea urchin eggs.

Sea urchin eggs emit light in the visible region during their fertilization. Judging from the chemiluminescence spectra, one of the excited species generated is considered to have originated from a tyrosine cation radical-mediated reaction. Chemiluminescence probes such as luminol or a cypridina luciferin analog (See text) are useful for detecting the ovoperoxidase +H2O2 reaction associated with membrane hardening and O2- generation, respectively, during fertilization of sea urchin eggs.

Mechanism of O2- generation in reduction and oxidation cycle of ubiquinones in a model of mitochondrial electron transport systems.

O2- generation in mitochondrial electron transport systems, especially the NADPH-coenzyme Q10 oxidoreductase system, was examined using a model system, NADPH-coenzyme Q1-NADPH-dependent cytochrome P-450 reductase. One electron reduction of coenzyme Q1 produces coenzyme Q1-. and O2- during enzyme-catalyzed reduction and O2+ coenzyme Q1-. are in equilibrium with O2- + coenzyme Q1 in the presence of enough O2. The coenzyme Q1-. produced can be completely eliminated by superoxide dismutase, identical to bound coenzyme Q10 radical produced in a succinate/fumarate couple-KCN-submitochondrial system in the presence of O2. Superoxide dismutase promotes electron transfer from reduced enzyme to coenzyme Q1 by the rapid dismutation of O2- generated, thereby preventing the reduction of coenzyme Q1 by O2-. The enzymatic reduction of coenzyme Q1 to coenzyme Q1H2 via coenzyme Q1-. is smoothly achieved under anaerobic conditions. The rate of coenzyme Q1H2 autoxidation is extremely slow, i.e., second-order constant for [O2][coenzyme Q1H2] = 1.5 M-1.s-1 at 258 microM O2, pH 7.5 and 25 degrees C.