2HIS:
reference: Insights into transition state stabilization of the beta-1,4-glycosidase Cex by covalent intermediate accumulation in active site mutants., Notenboom V, Birsan C, Nitz M, Rose DR, Warren RA, Withers SG, Nat Struct Biol 1998 Sep;5(9):812-8. PMID: 9731776

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