-0OC- pКа 3.2 -Co- CH pKa 4.& CH2 O *H,N-c-C H |
In proteins involved in blood clotting to heal a wound, the amino acid GLU is often chemically modified to carboxy-glutamic acid (abbreviated GLA, shown in diagram at pH 7) by a carboxylase enzyme in the blood. The pKa values for the two ionizable protons in the R-group of GLA are shown.
A sample of the octopeptide ILE-GLA-ARG-GLY-MET-ARG-PHE-SER was digested with trypsin, adjusted to pH 13, and applied to an anion exchange column. The peptides were then eluted from the column using a pH gradient from 13 to 0.5. Write the order of the products (no structures required) at the pH they would elute from the column and indicate the pH value. Assume pKa values for any newly generated a-amino and a-carboxyl groups are 9.6 and 2.2 respectively. (Relevant pKa values are 2.2, 3.2, 4.8, 9.6, and 12.5).
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