Rubisco
Introduction
Rubisco is a key protein in plants and some autotrophic bacteria, which functions as a catalysis in cellular metabolism, shows a wide variety of conservation from species to species and aids plants in survival under stressful conditions. Rubisco is used during the Calvin cycle of plants as a catalysis in CO2 fixation in which enzyme-bound ribulose -1, 5-bisphosphate to ribulose -1, 5-bisphosphate carboxylase/oxyegenase (Yoshizawa, 2004). Many plants use rubisco for metabolic purposes and its structural form and function is surprisingly mostly conserved in many plants (Yoshizawa, 2004). For example Form I rubisco, which is one of the most common forms among plants, consist of eight large and small subunits in a hexadecameric structure, is found in many CO2 fixing organisms, including all higher plants, algae, cyanobacteria and many autotrophic bacteria (Yoshizawa, 2004). Another form of rubisco called rubisco II thought only to be found in autotrophic bacteria has been found to be in many species now, showing that the rubisco proteins are even more conserved than once believed (Yoshizawa, 2004). The small sub units are encoded for by the nuclear DNA and the large sub units are encoded for in the chloroplast DNA. Light influences the expression of the gene.
Not only does rubisco serve a metabolic purpose it also helps the plant under stressful conditions caused by heat. An experiment on spinach leaves by Lixin Zhang and Eva Mari ARO called Rubisco activase: an enzyme with a temperature- dependent dual Function? The study found that during a sudden and unexpected exposure of a plant to heat stress, rubisco activase is likely to perform a second role as a chaperone in association with the thaylakoid bound ribosomes, possibly protecting them as a first aid in protecting thylakoid associated protein synthesis machinery against heat inactivation. (Rokka A., Lixin Zhang, L., ARO, E., 2001) This function of the rubisco might be caused by a conformational change due to heat, because it was found in the same study, that rubisco is better at catalyzing reactions at 42 degrees C than at 38- 40 degrees C, the changes in catalyzation rates were found to be due to a conformational change that rubisco undergoes when at these different temperatures, yet relatively close temperatures (Rokka A., Lixin Zhang, L., ARO, E., 2001).
In a paper “Mutagenesis at two distinct phosphate-binding sites unravels their differential roles in regulation of rubisco activation,” methods like the ones we used to isolate and located rubisco were used, in a study to find out the functional parts of rubisco. For example they used western blotting techniques and antibodies to locate the rubisco. There rubisco was purified in ammonium sulfate, in the presence of protease inhibitors; samples were ran in a western blot in which the gels were stained with comassie blue, proteins were located with a rabbit anti-rubisco serum (Marcus, 2005). The study also used methods not used in our experiments such as an X-ray analysis of tobacco which gave insight to the structure and functional sights of rubisco (Marcus, 2005).
In this experiment, it was decided to see if thicker leaves had more Rubisco in them than thinner leaves. It was thought that because thicker leaves were generally darker and had more mass; they would have more of the protein. The leaves that we tested were from a Tulip tree (Liriodendron tulipfera), a Magnolia (Magnolia grandifloria), a Red Maple (Acer rubrum), and a Sycamore (Platanus occidentalis).
