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Reactivity of the Cu II and tyrosyl free‐radical active site of the enzyme macromolecule galactose oxidase (goase)
Author(s) -
Wright Craig,
Sykes A. Geoffrey
Publication year - 2000
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/1521-3900(200007)156:1<263::aid-masy263>3.0.co;2-v
Subject(s) - galactose oxidase , stereospecificity , active site , chemistry , enzyme , stereochemistry , galactose , oxidase test , redox , substrate (aquarium) , macromolecule , selectivity , polymer chemistry , biochemistry , organic chemistry , catalysis , biology , ecology
Studies on the single Cu enzyme galactose oxidase (68kDa; 639 amino acids) from fungal Fusarium NRRL 2903 are considered. The enzyme reacts as a 2e − oxidase and catalyses the oxidation of primary alcohols such as D‐galactose, RCH 2 OH + O 2 → RCHO + H 2 O 2 . The Cu II , ∼8Å from the surface, is accessed by a channel which imposes stereospecific selectivity (e.g. no reaction is observed with L‐galactose). The Cu II is coordinated by Tyr‐272, Tyr‐495, His‐496, His‐581 and H 2 O (the substrate binding site) in a square pyramidal geometry. The active enzyme has a tyrosyl (Tyr) radical at 272, which together with the Cu II gives the required two‐equivalent redox activity. The active form of the enzyme, Goase ox , is reformed by the 2e − oxidation O 2 → H 2 O 2 . Acid‐base properties of the coordinated Tyr‐495 and H 2 O, and binding of NCS − , N 3 − , CH 3 CO 2 − and H 2 PO 4 in place of H 2 O are considered.