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1. Recent results suggest that the major flux is carried by a monomeric function, not by intermonomer electron flow. 2. The bifurcated reaction at the Qo-site involves sequential partial processes, - a rate limiting first electron transfer generating a semiquinone (SQ) intermediate, and a rapid second electron transfer in which the SQ is oxidized by the low potential chain. 3. The rate constant for the first step in a strongly endergonic, proton-first-then-electron mechanism, is given by a Marcus-Brønsted treatment in which a rapid electron transfer is convoluted with a weak occupancy of the proton configuration needed for electron transfer. 4. A rapid second electron transfer pulls the overall reaction over. Mutation of Glu-295 of cyt b shows it to be a key player. 5. In more crippled mutants, electron transfer is severely inhibited and the bell-shaped pH dependence of wildtype is replaced by a dependence on a single pK at ~8.5 favoring electron transfer. Loss of a pK ~6.5 is explained by a change in the rate limiting step from the first to the second electron transfer; the pK ~8.5 may reflect dissociation of QH·. 6. A rate constant (<103 s−1) for oxidation of SQ in the distal domain by heme bL has been determined, which precludes mechanisms for normal flux in which SQ is constrained there. 7. Glu-295 catalyzes proton exit through H+ transfer from QH·, and rotational displacement to delivers the H+ to exit channel(s). This opens a volume into which Q·− can move closer to the heme to speed electron transfer. 8. A kinetic model accounts well for the observations, but leaves open the question of gating mechanisms. For the first step we suggest a molecular “escapement”; for the second a molecular ballet choreographed through coulombic interactions.

Stationary dual-beam hydroacoustics and visual point count surveys were used in tandem to measure the density, target strength, and species composition of fishes associated with a petroleum platform in the northern Gulf of Mexico. Fish densities ranged from 0 to 10.5 fish · m-3 during monthly sampling trips from January 1991 to May 1992. Density and target strength were spatially and temporally variable. Target strengths varied significantly with side of the platform, month, and east and north current vectors. Density varied significantly with platform side, month, east current vector, and depth. Density and target strength did not change over 24 h periods or with water temperature. Fish densities were highest adjacent to the platform and decreased significantly beyond 16 m. Approximately 1990 - 28<|>100 fish were associated with the platform depending on the month. A total of 19 species were observed at the platform, with Chaetodipterus faber, Caranx fusus, Seriola dumerili, Balistes capriscus,Lutjanus campechanus, andArchosargus probatocephalus constituting 97% of observed fishes. Based on our results, we conclude that the fishes associated with a petroleum platform conform with the open nonequilibrium hypothesis proposed for fishes in coral reef habitats.

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