Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

James V. Moroney


Unicellular green algae, like Chlamydomonas reinhardtii, are able to grow photoautotrophically at low levels of CO$\sb2$. The efficient growth at low CO$\sb2$ levels is a reflection of the CO$\sb2$ concentrating mechanism that is induced when cells are adapted to low CO$\sb2$ levels. In this dissertation, the effect of CO$\sb2$ on carbonic anhydrase and other proteins in C. reinhardtii is discussed. In the first part of the dissertation, the isolation and purification of a new isoenzyme of carbonic anhydrase is reported. This carbonic anhydrase is present when cells are grown in high CO$\sb2$ but absent in low CO$\sb2$. It is located in the periplasm. N-terminal sequencing of the large and small subunit of this carbonic anhydrase showed that it is the protein product of the cah2 gene. In the second part of the dissertation, the effect of light and CO$\sb2$ on rubisco activase and carbonic anhydrase was examined. In C. reinhardtii, rubisco activase induction is unaffected by CO$\sb2$ concentration and carbon source. However, the level of this protein and its transcript levels oscillate when placed under a twelve hour light, twelve hour dark growth regime. Like rubisco activase, transcript levels of carbonic anhydrase oscillate throughout the light and dark cycle and the transcript is present in the dark. The requirement for light for the induction of carbonic anhydrase was tested in C. reinhardtii cells grown synchronously. In contrast to asynchronously grown cells, carbonic anhydrase was induced by low CO$\sb2$ levels in the absence of light in synchronously grown cells. In the third part of the dissertation, one of the proteins that appears transiently when C. reinhardtii cells are adapted to air was shown to be a degradation product of the large subunit of rubisco. The degradation of rubisco may play a role in the change in pyrenoid morphology that occurs during the induction of the CO$\sb2$ concentrating mechanism. The N-terminal sequence of another protein that is induced by low CO$\sb2$ was presented.