The path of carbon in photosynthesis—Back to the future

Abstract

F ive to ten billion tons of carbon dioxide from fossil-fuel based energy production and from deforestation burnoff are entering the atmosphere annually. Suggested solutions to this massive accumulation include alternate energy sources, energy conservation, massive reforestation and, in the long term, increased use of natural carbon dioxide reservoirs such as the oceans. Relatively neglected in global planning efforts are the opportunities which may lie in the genetic engineering of the two key enzymes in photosynthetic carbon dioxide fixation, phosphoribulokinase (PRK) and ribulosebisphosphate carboxylase/oxygenase (Rubisco). Even the smallest increase in the efficiency of CO 2 fixation by Rubisco would remove significant amounts of CO 2 from the atmosphere. (A 1% increase on a worldwide basis would theoretically fix 1.5.109 additional tons of CO 2 per year. It is estimated that 1.5.1011 tons of CO 2 are sequestered annually by photosynthesis.) Present funding in this area is modest by any standards and it is surprising that a concerted research program to achieve both an understanding and enhancement of the Rubisco reaction has not been implemented nor, perhaps, even seriously considered at a national level. With this in mind, the purpose of this review is to detail the background and research which led to the first isolation and characterization