Laser-Activated Electron Transport in a Chlamydomonas Mutant

Abstract

Following laser activation of electron transport in the pale green mutant of Chlamydomonas reinhardii, the following kinetics are observed: a rapid absorption decrease at 421 m[mu] (half-time < 2 x 10-6 sec) recovering with a half-time of[long dash]7 x 10-3 sec.; oxidation of cytochrome f at 554 m[mu] with a half-time of 1 x 10-4 sec.; oxidation of cytochrome of type b, at 432 and 564 m[mu], with a half-time of [long dash] 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 [reverse arrow] cytochrome f [reverse arrow] [reverse arrow] 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.