I. Rojdestvenski et al., A carbonic anhydrase catalyzed CO2 pump in Chlamydomonas reinhardtii: In vivo experiments, computer modelling, and theory, RUSS J PL P, 47(5), 2000, pp. 613-621
We studied the bicarbonate depletion effects on photosynthesis in high-CO2
grown-cell wall-less mutants of Chlamydomonas reinhardtii with (cw92) and w
ithout (cia3/cw15) active carbonic anhydrase (CA) associated with photosyst
em II (PSII). The mutants were grown in a high-CO2 medium and then washed w
ith a CO2-free buffer. We discuss the shutdown of oxygen evolution in cw92
as a consequence of CO2 depletion of the Calvin cycle. It is suggested that
CA acts as part of a PSII-driven pump delivering CO2 from the lumen into t
he stroma, where it becomes available to the Calvin cycle. Our model is sup
ported by computer simulation data and accommodates the results of in vivo
experiments as well as the differences between cw92 and cia3 mutants. We al
so present a simple theory of the phenomena discussed, based on a time-scal
e hierarchy approach, which describes the CO2 depletion in cw92 using only
two rate constants-V-max and K-m of the Calvin cycle.