Effects of DCMU and Antimycin A on Photoassimilation of Glucose in Chlorella.

TI1vwo basically differenlt svstemlls have been described by which chloroplast preparations are able to synthesize ATP in the light: cyclic and nioncyclic photophosphorylation (2, 3). Other systems producing ATP in the light. e.g. pseudocyclic (or aerobic) anid oxidative photoplhosphorylatioins might only be variations of the 2 basic types (26. 27). A main feature of true cyclic photophosphorylatioln in chloroplasts is its resistanice to DCMU3 anid CMLU (16), inhibitors of photosynithetic O. productioni (5, 29). According to the conicept of 2 light reactionls in p)hotosynthesis (8. 11, 1.5 32) this DCIUIU resistanice imieanis that cyclic photophosphorvlation should be driveni onily by the first light reaction an(l lnot depend( onl the seconid onle, hich is responsible for the splitting of water. Such evidenice has been obtained by Tagawa et al. (22) for ferredoxinicatalyzed cyclic photophosphorylation in chloroplast l)reparations. In spite of a vast literature oni photophosphorylation in vitro, much less is known about photophosphorvlation in vivo. The best evidenice for photophosphorylation in vivo has beeln obtained by following glucose assimilationi of Chilorclla (13, 14) anid of leaf (liscs (18). acetate assimiiilation of Chlamiivdobotrys (19,31), inhibitioni of photoreduction bv glucose in A4ikistzrodcsimts (6), and light-enhanced P32 incorporationi in Hclodea denisa (20). In the followinig paper the question was inivestigated whether cyclic photophosphorylation of the tvpe observed in chloroplasts also occurs in vivo. The influence of DCMIU and anitimycin A onl light dependent glucose assimilatioIn in Cliloriella was sttl(lied in the absenice of CO.. anid 0.,