Factor VIIa: Difference between revisions

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	====One-proton versus Two-proton transfer====		====One-proton versus Two-proton transfer====
	The charge relay system explains the action of Ser344 as part of resonance forms Asp-CO2-/H-His/Ser-OH and Asp-CO2H/His-H/Ser-Owhich involve proton transfers between Ser344 to His193 and His193 to Asp242. However this two-proton transfer mechanims		The charge relay system explains the action of Ser344 as part of resonance forms Asp-CO2-/H-His/Ser-OH and Asp-CO2H/His-H/Ser-Owhich involve proton transfers between Ser344 to His193 and His193 to Asp242. However this two-proton transfer mechanims requires that the pKa of His344 is lower than pKa of Asp242. The argument for one-proton transfer mechanism, supported by 1H NMR experiments, observed the pKa of free enzyme and acylenzyme His344 to be ~7 whereas that of tetrahedral intermediate to be more than 10. This argues for stabilization of protonated His344 by the negatively charged Asp242 or a one-proton transfer mechanims<ref>PMID:12475199</ref>.

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