The mechanism of hydrogen photoproduction by several algae : I. The effect of inhibitors of photophosphorylation.

In order to come to a more firmly based conclusion on the mechanism of hydrogen photoproduction in green algae, we have compared two additional genera of green algae, i.e., Ankistrodesmus and Chlorella, with the previously tested Chlamydomonas and Scenedesmus. None of the algae tested required photosystem II for H2 photoproduction, since this reaction still occurred in the presence of 10(-5)M DCMU. Photophosphorylation was also not required since two potent inhibitors of this process, Cl-CCP and SAL, almost always stimulated H2 photoproduction. However, the effect of the inhibitors was found to vary with the species of alga and also with the age and growth conditions of the culture. The highest concentration of SAL tested (10(-2)M) always stimulated H2 photoproduction by photoheterotrophically grown cells, but often inhibited this reaction in autotrophically grown cells. When present, this inhibition by SAL was associated with gross pigment damage. The variation in the effect of Cl-CCP upon H2 photoproduction due to different growth conditions was particularly striking for Chlorella vulgaris.Cl-CCP gave very little if any stimulation of this reaction in autotrophically grown cells of this alga, but stimulated H2 photoproduction by photoheterotrophically grown cells approximately 450%. Chlamydomonas cells were found to be about ten times as sensitive as the other cells to both poisons. We conclude that all of the algae tested are able to photoproduce H2 via non-cyclic electron flow through photosystem I to hydrogenase.