Sandbox Reserved 640: Difference between revisions
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In opposition to the differences in polypeptides among globin proteins (Hemoglobin and Myoglobin), the heme group has been found to remain largely the same<ref name=a />. The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring counterparts. The way the heme group attaches to the polypeptide is also different. The steric crowding around the ligand binding site (beside the heme) is reduced, plus there is an altered packing at the proximal side of the heme and conformational differences along the distal side. As a result, the oxygen affinity is larger than that of Myoglobin and Hemoglobin <ref name=eight>Ellis, P. J., C. A. Appleby, J. M. Guss, W. N. Hunter, D. L. Ollis, and H. C. Freeman. "Structure of Ferric Soybean LeghemoglobinNicotinate at 2.3 Å Resolution." Acta Crystallographica Section D Biological Crystallography 53.3 (1997): 302-10. Print.</ref>. This is reflected by the Km of 0.01 microM (the concentration for half of the Leghemoglobin to be saturated with dioxygen), about ten times the Michaelis constant for Hemoglobin <ref name=seven />). | In opposition to the differences in polypeptides among globin proteins (Hemoglobin and Myoglobin), the heme group has been found to remain largely the same<ref name=a />. The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring counterparts. The way the heme group attaches to the polypeptide is also different. The steric crowding around the ligand binding site (beside the heme) is reduced, plus there is an altered packing at the proximal side of the heme and conformational differences along the distal side. As a result, the oxygen affinity is larger than that of Myoglobin and Hemoglobin <ref name=eight>Ellis, P. J., C. A. Appleby, J. M. Guss, W. N. Hunter, D. L. Ollis, and H. C. Freeman. "Structure of Ferric Soybean LeghemoglobinNicotinate at 2.3 Å Resolution." Acta Crystallographica Section D Biological Crystallography 53.3 (1997): 302-10. Print.</ref>. This is reflected by the Km of 0.01 microM (the concentration for half of the Leghemoglobin to be saturated with dioxygen), about ten times the Michaelis constant for Hemoglobin <ref name=seven />). | ||
The methods by which various Leghemoglobins were purified, and then analyzed, are as follows: | The methods by which various Leghemoglobins were purified, and then analyzed, are as follows<ref name=a>: | ||
*Ammonium Sulfate Precipitation | *Ammonium Sulfate Precipitation | ||
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*Isoelectrofocusing | *Isoelectrofocusing | ||
*Nuclear Magnetic Resonance (NMR) | *Nuclear Magnetic Resonance (NMR) | ||
*X-ray crystallography | *X-ray crystallography | ||
==Mechanism== | ==Mechanism== | ||
Because Leghemoglobin can autooxidize, there are several mechanisms to maintain the protein in its active (reduced) form. One of them involves an enzyme called, Leghemogobin Reductase. This protein is a flavoprotein that catalyzes the reduction of Lb<sup>3+</sup> (ferric form) to Lb<sup>2+</sup> (ferrous form) using NADH. The reaction is as follows: | Because Leghemoglobin can autooxidize, there are several mechanisms to maintain the protein in its active (reduced) form. One of them involves an enzyme called, Leghemogobin Reductase<ref name=a>. This protein is a flavoprotein that catalyzes the reduction of Lb<sup>3+</sup> (ferric form) to Lb<sup>2+</sup> (ferrous form) using NADH. The reaction is as follows: | ||
<div style="text-align: center;"> NAD(P)H + H+ + 2 ferrileghemoglobin NAD(P)+ + 2 ferroleghemoglobin </div> | <div style="text-align: center;"> NAD(P)H + H+ + 2 ferrileghemoglobin NAD(P)+ + 2 ferroleghemoglobin </div> | ||
Ferric Leghemoglobin can also be reduced to the ferrous form by free flavins in the presence of NADH or NADPH. Lastly, Leghemoglobin can be reduced to its ferrous form directly by physiological reductants. These reductants are various electron donors commonly found in plant cells, which reduce the Leghemoglobin nonenzymatically. | Ferric Leghemoglobin can also be reduced to the ferrous form by free flavins in the presence of NADH or NADPH. Lastly, Leghemoglobin can be reduced to its ferrous form directly by physiological reductants. These reductants are various electron donors commonly found in plant cells, which reduce the Leghemoglobin nonenzymatically.<ref name=b>. | ||
==Notes== | ==Notes== | ||
{{reflist}} | {{reflist}} | ||
