Oxygenase and Carboxylase Activities of RuBP Carboxylase from Wheat Leaves

The oxygenase reaction catalysed by RuBP carboxylase initiates a metabolic sequence responsible for photorespiration (Bowes et al. 1972). Studies with inhibitors and with mutants show that control of photorespiration can have beneficial effects only if it is achieved by decreasing the oxygenase activity of RuBP carboxylase (Servaites, Ogren, 1977; Somerville, Ogren, 1982). No corroborated evidence is available for carboxylation of RuBP without susceptibility to oxygenation. If oxygenase activity and photorespiration have a function in plants, then regulation by changing levels of metabolic intermediates might be expected. This was investigated in a test system containing purified RuBP carboxylase from wheat with RuBP and rate-limiting concentrations of HCO3 − and O2. The sensitivity of the ratio vc:vo to pH (CO2 concentration), the presence of carbonic anhydrase (CO2 availability) and the presence of Mn2+ is illustrated to validate the methods used. RESP-8916