chem research paper 1

Above the zinc ion in the active site of the enzyme

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Unformatted text preview: as the other displayed in Figure 5. This example exemplifies that although the active sites of the enzyme may very, the general process of the enzyme stays constant as well as its ability to perform, however it affects its productivity. Like discussed above, the zinc ion in the active site of the enzyme can be replaced with other metal ions, like cadmium and cobalt. Although cobalt is very unlikely found in metalloenzymes, it is used frequently as a spectroscopic probe in zinc metalloproteinsxi. Cobalt can be substituted into native carbonic anhydrase with the tetrahedrally coordinated zinc (II) to yield an active enzyme. However cobalt has a long electron spin relaxation ground state, which leads it to be less effective. To counter this, several anion inhibitors bind to the metal to create low lying excited energy states that create large dipole shifts to active site residues to increase productivity. xi To empirically confirm this, the scientists use x-ray structure analysis to compare the bovine enzyme and the cobaltcoordinated enzyme. Their findings found that this bonding induced small changes in the arrangement of the residues in the active site cavity, the area that is associated with the proton transfer mechanism of the enzyme. xi The data is displayed in Figure 6. This is one example of how ion substitution can be used effectively without drastic change to the carbonic anhydrase function. Like cobalt, cadmium is also a possible substitute for zinc in the active site of the carbonic anhydrase. Cadmium is highly associated with the enzyme in marine life, specifically the marine diatom Thalassiosira weissflogii.xii This is due to the fact that organic matter has a higher fractionation of light cadmium isotopes due to the uptake of cadmium in marine organisms.xiii This cadmium-bounded enzyme is a structural mimic of the function beta carbonic anhydrase dimer with high resemblance for the active site residue location as shown in Figure 7. ‘ Due to the structural similarity, it suggest that there is a common catalytic mechanism and this is also proven by the location of the metal bound ion within its tetrahedrally bound water molecule which are nearly identical and the role of the amino acids Asp-Arg are also identicalxiv. The mimicry between the two suggests that there is a complete active site. The mimicry also suggests that there is reason for spontaneous exchange between zinc and cadmium. xiv To clarify, the conserved sequences between the two conformers allow a stable open confirmation, which lowers the free energy penalty and lets the metals exchange positions. xiv This study confirms that the cadmium bound enzyme is an efficient form of the enzyme in marine life situations. Another more in depth study examines the coordination of the cadmium bound carbonic anhydrase (carbonate complex) with an alkythiolate ligand. xii Through NMR and MS analysis, it was found that the cadmium enzyme supported efficient carbonate formation with the new alkythiol...
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This note was uploaded on 10/01/2013 for the course CHEM 305 taught by Professor Mcnamara during the Spring '13 term at William & Mary.

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