Question

When homoglobin shift from T state to R state, Why the bond between His HC3 and Asp FG1 is broken and His HC3 rotate toward the center of the molecule? What factors break the bond between His and Asp? By the way , for His HC3, what does the HC3 mean? thanks a lot

Answer 1

The T (tensed, deoxygenated) to R (relaxed, oxygenated) transition is trigerred by change in the positions of amino acid side chains which surround the heme group.In the T state, the porphyrin is slightly puckered which causes the heme iron to protrude on the proximal His. side. The binding of O2 causes the heme to take a more planar conformation, shifting the position of the proximal His and the attached F helix. These changes lead to adjustments in the ion pairs.

Factors that break the bond between His and Asp:

-increased pH

-combining with oxygen (iron heme group moves from the outside to the inside)

-protonation of Histidine

HC3= It is the carboxyl-group of the beta subunit. Its position on Histidine amino acid is 146.