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. Author manuscript; available in PMC: 2019 Feb 14.
Published in final edited form as: Chem Rev. 2017 Jul 12;118(3):1169–1198. doi: 10.1021/acs.chemrev.7b00123

Figure 22.

Figure 22

QSOX catalytic cycle. This model depicts turnover involving two-electron reduced forms of the enzyme for simplicity. Additional pathways involving four-electron reduced enzyme forms may contribute at high concentration of reducing substrates and/or low oxygen tensions. Curved lines represent motion. Step 1 is reduction of QSOX by substrate protein. Step 2 is the rapid formation of an interdomain disulfide. Step 3 is a rate limiting step involving reduction of the flavin cofactor. Step 4 regenerates the oxidized enzyme and occurs from either the closed or the open (shown here) state.