The C-2 oxidative photosynthetic carbon cycle

The C-2 oxidative photosynthetic carbon cycle plus the C-3 reductive photosynthetic carbon cycle coexist. Both are initiated by Rubisco, use about equal amounts of energy, must regenerate RuBP, and result in exchanges of CO2 and O-2 to establish rates of net photosynthesis, CO2 and O-2 compensation points, and the ratio of CO2 and O-2 in the atmosphere. These concepts evolved from research on O-2 inhibition, glycolate metabolism, leaf peroxisomes, photorespiration, O-18(2)/O-16(2) exchange, CO2 concentrating processes, and a requirement for the oxygenase activity of Rubisco. Nearly 80 years of research on these topics are unified under the one process of photosynthetic carbon metabolism and its self-regulation.