The control of carbon dioxide assimilation and ribulose 1,5-diphosphate carboxylase activity in Anacystis nidulans grown in a light-limited chemostat.

The blue-green alga, Anacystis nidulans, was grown in a light-limited chemostat at specific growth rates ranging from 0.02 h-1 to 0.10h-1. The rate of carbon dioxide assimilation, measured under optimal experimental conditions, increased 3 to 5 fold with increasing growth rate over this range. Ribulose 1,5-diphosphate carboxylase (RuDPCase) activity per organism increased four fold over the same growth rate range. RuDPCase specific activity in terms of total protein remained constant at all growth rates. The total protein content per organism and the percentage of protein in the dry weight increased in faster growing organisms. The dry weight per organism also increased as growth rate increased. These results are discussed to show that RuDPCase activity is not controlled by transcriptional mechanisms but that its activity per cell is regulated by gene dosage.