by daywalker20 » Thu Aug 05, 2010 6:09 am
hey....
The ability of photosynthetic organisms to use CO2 for photosynthesis depends in part on the properties of Rubisco. Rubisco has a surprisingly poor affinity for CO2, probably because it evolved in an atmosphere that had very high CO2 levels compared with the present atmosphere. In C3 plants the Km(CO2) of Rubisco ranges between 15 and 25 µM. In cyanobacteria Rubisco has an even lower affinity for CO2, and the Km(CO2) can be greater than 200 µM. In comparison, the concentration of CO2 in water in equilibrium with air is approximately 10 µM. From these numbers it becomes apparent that Rubisco is operating at no more than 30% of its capacity under standard atmospheric conditions. This is one of the reasons that C3 plants contain such large amounts of Rubisco. Exacerbating this situation is the fact that O2 is a competitive substrate with respect to CO2.