Binding studies were carried out in which heparin was immobilized on the surface of cuvettes. The pH dependence of HPRG binding to heparin was investigated and the results are shown in Figure.

a. How is the binding of HPRG to heparin dependent on pH? Give structural reasons for the binding dependence. The structure of heparin is shown in Figure

2.2. NOTE: Figure also serves as a titration curve for the His residues in HPRG-what is the pKR for these residues? Explain.

b. The same binding studies were carried out in which HPRG was reacted with diethylpyrocarbonate (DEPC), a compound that specifically reacts with histidine residues. The reaction is shown in figure. Explain the results.