Fumarase is an enzyme that catalyzes the reaction of malate to fumarate, and of fumarate to malate. The fumarase enzyme being observed here is fumarase C, from e. coli. There are two possible active sites that are found in fumarase, both containing carboxylic acid binding sites. These sites are known as the A site and B site. The key residue in both sites is a histidine residue, which can interact with water and can participate in base catalysis. To determine the actual active site of fumarase, Weaver[1]. changed the important histidine residue in each possible active site to an asparagine. The experiment measured the specific activity, average activity, and average protein concentration of fumarase upon altering each possible active site individually. The results of the experiment for the mutated fumarase enzymes were compared to that of a wild type enzyme, and the data showed the H129N mutant had similar specific activities to the wild type, but the H188 mutant had a significantly lower specific activity than H129N or wild type. These results show that the active site is the A site because a mutation of H188 yielded significantly reduced enzymatic activity. The mutation of H129N showed small differences in enzymatic activity compared to the wild type fumarase, which further suggests that the B site is not the true active site. [2].
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Structural highlights
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