Factor VIIa: Difference between revisions

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====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~~ 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>.

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-O which involve proton transfers between Ser344 to His193 and His193 to Asp242. However this two-proton transfer mechanim 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 electrostatic stabilization of protonated His344 by the negatively charged Asp242 or a one-proton transfer mechanims<ref>PMID:12475199</ref>.

====Low barrier hydrogen bonds====

The hydrogen bond between Asp242 and His344 has been suggested to fulfill many criteria for low barrier hydrogen bond. This criteria includes a <2.6Ǻ distance between Asp242 and His344,an unusually downfield signal of the Nδ1 proton of His344 in 1H NMR, an observed deuterium isotope effect, and a low D/H fractionation factor of the Nδ1 proton<ref>PMID:7661899</ref>.

Factor VIIa: Difference between revisions

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@@ Line 28: / Line 28: @@
 ====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 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>.
+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-O which involve proton transfers between Ser344 to His193 and His193 to Asp242. However this two-proton transfer mechanim 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 electrostatic stabilization of protonated His344 by the negatively charged Asp242 or a one-proton transfer mechanims<ref>PMID:12475199</ref>.
+====Low barrier hydrogen bonds====
+The hydrogen bond between Asp242 and His344 has been suggested to fulfill many criteria for low barrier hydrogen bond. This criteria includes a <2.6Ǻ distance between Asp242 and His344,an unusually downfield signal of the Nδ1 proton of His344 in 1H NMR, an observed deuterium isotope effect, and a low D/H fractionation factor of the Nδ1 proton<ref>PMID:7661899</ref>.