What role does substrate concentration play in Rubisco binding to CO2 or O2?

Substrate concentration plays a crucial role in the catalytic activity of the enzyme Rubisco, particularly in relation to its binding with carbon dioxide (CO2) and oxygen (O2). Higher concentrations of CO2 increase the likelihood of Rubisco binding to CO2 due to the basic principles of enzyme-substrate interactions. When CO2 is more abundant, there is an increased probability that it will encounter and bind to the active sites of Rubisco, facilitating the carboxylation reaction that leads to the formation of carbohydrates during photosynthesis. This saturation effect enhances the overall rate of the Calvin cycle.

In contrast, if O2 concentrations were to rise, it would not promote the binding of CO2; instead, it may lead to a process known as photorespiration, where Rubisco can mistakenly bind oxygen rather than carbon dioxide. Therefore, the dynamics between CO2 and O2 concentrations significantly influence the functionality of Rubisco and subsequently the efficiency of photosynthesis. This concept highlights the competitive nature of substrate binding in enzymatic reactions.