Rubisco also catalyzes RuBP with oxygen () in an interaction called photorespiration, a process that is more prevalent at high temperatures. During photorespiration RuBP combines with  to become 3-PGA and . Like the Calvin-Benson Cycle, the photorespiratory pathway has been noted for its enzymatic inefficiency although this characterization of the enzymatic kinetics of rubisco have been contested. Due to enhanced RuBP carboxylation and decreased rubisco oxygenation stemming from the increased concentration of  in the bundle sheath, rates of photorespiration are decreased in  plants. Similarly, photorespiration is limited in CAM photosynthesis due to kinetic delays in enzyme activation, again stemming from the ratio of carbon dioxide to oxygen.