User:J. Shaun Lott/BIOSCI 203: Difference between revisions
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hORF6 is an example of a 1-Cys Prx, and central to its enzymatic activity is its ability to maintain the active site cysteine residue in the charged (deprotonated) form of a thiolate ion (-S<sup>-</sup>) rather than the usual uncharged (protonated) sulfhydryl form (-SH). | hORF6 is an example of a 1-Cys Prx, and central to its enzymatic activity is its ability to maintain the active site cysteine residue in the charged (deprotonated) form of a thiolate ion (-S<sup>-</sup>) rather than the usual uncharged (protonated) sulfhydryl form (-SH). | ||
Use the Henderson-Hasselbach equation to answer the questions below. The p<i>K</i><sub>a</sub> of the –SH group of free cysteine is 8.5. The cytosol of human cells is normally at pH 7.3. | Use the Henderson-Hasselbach equation to answer the questions below. The p<i>K</i><sub>a</sub> of the –SH group of free cysteine is 8.5. The cytosol of human cells is normally at pH 7.3. The p<i>K</i><sub>a</sub> of the active site cysteine in a 1-Cys Prx enzyme has been measured at 6.0. | ||
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Q4: What would be the % ionization of the –SH group of free cysteine in the cytosol? | Q4: What would be the % ionization of the –SH group of free cysteine in the cytosol? | ||
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Q5: What would be the % ionization of the –SH group of the Prx active site cysteine in the cytosol? | Q5: What would be the % ionization of the –SH group of the Prx active site cysteine in the cytosol? | ||
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Now let’s look at the structure to see if we can identify what features of the hORF structure may influence the ability of the active site cysteine to ionize. | Now let’s look at the structure to see if we can identify what features of the hORF structure may influence the ability of the active site cysteine to ionize. | ||
<applet load="HORF6.pdb" size="500" color="white" frame="true" align="left" caption="Active site" /> | |||