Enzyme Levels in Relation to Obligate Phototrophy in Chlamydobotrys

During the transition from photoheterotrophic growth on acetate to phototrophic growth on carbon dioxide, there is a decrease in isocitrate lyase and increase in ribulose-1,5-diphosphate carboxylase activity in Chlamydobotrys stellata cultures. The increase in ribulose-1,5-diphosphate carboxylase activity is the result of protein synthesis, there being a close correlation between increase in enzyme activity and protein precipitated by antibody to ribulose-1,5-diphosphate carboxylase. The purified ribulose-1,5-diphosphate carboxylase was similar to the constitutive enzyme from other green algae having a molecular weight of 530,000 and composed of two types of subunit of molecular weight 53,000 and 14,000.Enzyme assays demonstrated an incomplete tricarboxylic acid cycle in cells growing photoheterotrophically on acetate or phototrophically on carbon dioxide. Although these cells lack alpha-ketoglutarate dehydrogenase and succinate thiokinase, a cyclic flow of acetate carbon is possible in the presence of the glyoxylate cycle enzymes but the yield of adenosine triphosphate from acetate oxidation may be insufficient to support heterotrophic growth, so rendering Chlamydobotrys an obligate phototroph.