Laser-activated electron transport in a Chlamydomonas mutant.

Following laser activation of electron transport in the pale green mutant of Chlamydomonas reinhardii, the following kinetics are observed: 1) A rapid absorption decrease at 421 mmu (half-time < 2 x 10(-6) sec) recovering with a half-time of approximately 7 x 10(-3) sec. 2) Oxidation of cytochrome f at 554 mmu with a half-time of 1 x 10(-4) sec. 3) Oxidation of cytochrome of type b, at 432 and 564 mmu, with a half-time of approximately 6 x 10(-3) sec, following a 2 x 10(-3) sec lag. THE RESULTS ARE INTERPRETED ACCORDING TO A LINEAR ELECTRON TRANSPORT SEQUENCE: system I trap <-- cytochrome f <-- <-- cytochrome b with an additional molecule of cytochrome b in the cyclic photophosphorylation pathway. Experiments with uncouplers provide evidence for a site of photophosphorylation between cytochrome f and cytochrome b. Additional studies involve inhibitors of electron transport, the temperature dependence and quantum efficiency of cytochrome oxidation, and the effect of oxygen and pre-illumination on the laser-induced absorption changes.