“…The so called ''photoreduction'', i.e. the reduction of CO 2 at the expense of hydrogen in hydrogenase adapted algae (Gaffron 1940), was not inhibited by DCMU, resembling the phototoreduction of manganese in Mn-depleted algae (Pirson 1937), Mn is since known to be involved in oxygen evolution. Cyclic photophosphorylation, as discovered by Arnon et al (1954) was found by Jagendorf and Avron (1959) neither to be inhibited by DCMU, nor was the first artificial donor system for NADP reduction-DCPIP/ascorbate (Vernon and Zaugg 1960).…”