Quo vadis photorespiration: A tale of two aldolases

An O-2-consuming side reaction of D-ribulose 1,5-bisphosphate carboxylase causes photorespiration in plants. This reaction may be an inevitable consequence of the enzyme's inability to protect its ene-diolate reaction intermediate from O-2, a notion that is supported by the failure of persistent efforts to eliminate selectively its oxygenase activity by genetic manipulation, We have examined two aldolases with similar ene-diolate intermediates, L-rhamnulose l-phosphate aldolase and L-fuculose l-phosphate aldolase, The former enzyme has an oxygenase activity, while the latter does not, suggesting that the reaction with O-2 is not inevitable.