Ribonuclease A is the oldest model for studying enzymatic mechanisms, yet questions remain about proton transfer within the active site. Seminal work by Jackson (Science, 1994) labeled Ribonuclease A with 4-fluorohistidine, concluding that active-site histidines act as general acids and bases. Calculations of 4-fluorohistidine indicate that the π-tautomer is predominant in all simulated environments (by ~17 kJ/mol), strongly suggesting that fluoro-labeled ribonuclease A functions with His119 in π-tautomer. The tautomeric form of His119 during proton transfer and tautomerism as a putative mechanistic step in wild-type RNase A remain open questions and should be considered in future mechanistic studies.
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| http://dx.doi.org/10.1016/j.cplett.2016.10.072 | DOI Listing |
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