in extant Rubiscos that bind a small subunit. C4 With the mass convergent evolution of the C4-fixation pathway in a diversity of plant lineages, ancestral C3-type RuBisCO evolved to have faster turnover of in exchange for lower specificity as a result of the greater localization of from the mesophyll cells into the bundle sheath cells. This was achieved through enhancement of conformational flexibility of the “open-closed” transition in the Calvin Cycle. Laboratory-based phylogenetic studies have shown that this evolution was constrained by the trade-off between stability and activity brought about by the series of necessary mutations for C4 RuBisCO. Moreover, in order to sustain the destabilizing mutations, the evolution to C4 RuBisCO was preceded by a period in which mutations granted the enzyme increased stability, establishing a buffer to sustain and maintain the mutations required for C4 RuBisCO. To assist with this buffering process, the newly-evolved enzyme was found to have further developed a series of stabilizing mutations. While RuBisCO has always been accumulating new mutations, most of these mutations that have survived have not had significant effects on protein stability. The destabilizing C4 mutations on RuBisCO has been sustained by environmental pressures such as low concentrations, requiring a sacrifice of stability for new adaptive functions. History of the term The term "RuBisCO" was coined humorously in 1979, by David Eisenberg at a seminar honouring the retirement of the early, prominent RuBisCO researcher, Sam Wildman, and also alluded to the snack food trade name "Nabisco" in reference to Wildman's attempts to create an edible protein supplement from tobacco leaves. The capitalization of the name has been long debated. It can be capitalized for each letter of the full name (Ribulose-1,5 bisphosphate carboxylase/oxygenase), but it has also been argued that is should all be in lower case (rubisco), similar to other terms like scuba or laser. See also Carbon cycle Photorespiration Pyrenoid C3 carbon fixation C4 carbon fixation Crassulacean acid metabolism/CAM photosynthesis Carboxysome References Further reading External links Photosynthesis EC 4.1.1