Rubisco, an old challenge with new perspectives.

The importance of Rubisco derives from its spe­ cial role as the main catalyst for the flow of carbon dioxide from the inorganic sphere to the plant kingdom. Since its discovery as fraction I protein fifty years ago (Wildman and Bonner, 1947) and its role as the key enzyme in the Calvin cycle forty years ago (Quaile et al., 1954; Weissbach et al., 1954) it attracted attention for a series of specific reasons concerning its enzyme mechanism, its reg­ ulation and its structural features. Twentyfive years ago the bifunctionality of this enzyme was discovered by the fact that it catalyses not only C 0 2 fixation but also the RuBP oxygenase reac­ tion, and therefore, Rubisco is also the key en­ zyme for the photorespiration (Bowes et al., 1971). Since photorespiration is generally considered a wasteful process due to the loss of fixed carbon and the additional consumption of energy, parti­ tioning of carbon between Calvin cycle and the photorespiratory pathways plays a crucial role in the efficiency of photosynthesis (Zelitch, 1973). The predominant role of this enzyme as an im­ portant research area in plant biochemistry can be illustrated by the vast and still growing number of communications of sequence data (above 1500) and of twelve reports of X-ray structures (enzymes from photosynthetic bacteria, cyanobacteria and higher plants). The recent renaissance of Rubisco research should lead to a better understanding of its mechanisms of function by a combined effort