Photorespiration: The Futile Cycle?

Photorespiration, or C-2 photosynthesis, is generally considered a futile cycle that potentially decreases photosynthetic carbon fixation by more than 25%. Nonetheless, many essential processes, such as nitrogen assimilation, C-1 metabolism, and sulfur assimilation, depend on photorespiration. Most studies of photosynthetic and photorespiratory reactions are conducted with magnesium as the sole metal cofactor despite many of the enzymes involved in these reactions readily associating with manganese. Indeed, when manganese is present, the energy efficiency of these reactions may improve. This review summarizes some commonly used methods to quantify photorespiration, outlines the influence of metal cofactors on photorespiratory enzymes, and discusses why photorespiration may not be as wasteful as previously believed.

Automated summary

Photorespiration, also known as C-2 photosynthesis, is often seen as a futile cycle that can reduce carbon fixation during photosynthesis. However, many essential processes rely on photorespiration, and enzymes involved in these reactions can interact with manganese in addition to magnesium. This review discusses the methods used to quantify photorespiration, the impact of metal cofactors on photorespiratory enzymes, and challenges the idea that photorespiration is as wasteful as previously believed.