Enzyme Levels in Relation to Obligate Phototrophy in Chlamydobotrys

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Abstract
During the transition from photoheterotrophic growth on acetate to phototrophic growth on CO2, there is a decrease in isocitrate lyase and increase in ribulose-1,5-diphosphate carboxylase activity in C. 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 have a MW of 530,000 and composed of 2 types of subunit of MW 53,000 and 14,000. Enzyme assays demonstrated an incomplete tricarboxylic acid cycle in cells growing photoheterotrophically on acetate or phototrophically on CO2. Although these cells lack .alpha.-ketoglutarate dehydrogenase and succinate thiokinase, a cyclic flow of acetate C is possible in the presence of the glyoxylate cycle enzymes but the yield of ATP from acetate oxidation may be insufficient to support heterotrophic growth, so rendering Chlamydobotrys an obligate phototroph.
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