ABSTRACT
Light of low intensity (less than or equal to 25-10(5) erg-cm(-2)-sec(-1)) stimulates hydrogen production by cell suspensions of Anabaena variabilis in the presence of glucose, pyruvate or formate. The maximum rate of hydrogen production in the presence of these substrates was observed at light intensities of 650, 1400 and 2250 erg-cm(-2)-sec(-1), respectively. The rate of oxygen production by the cells increases while the rate of hydrogen evolution decreases with increase in light intensity (2.5-6.0-10(3) erg-cm(-2)-sec(-1)). In the presence of DCMU (10(-5)-10(-4) M), hydrogen evolution is not inhibited in the presence of pyruvate or formiate and is inhibited to a less extent in the presence of glucose. According to the results obtained, hydrogen evolution by A. variabilis in the light does not require the action of two photosystems. Inhibition of hydrogen production at significant light intensities is due to the action of oxygen on this process; the rate of oxygen evolution increases with light intensity.
