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. 2023 Sep 16;14:5752. doi: 10.1038/s41467-023-41533-x

Fig. 6. Functional role of Y244 during the CcO reaction cycle.

Fig. 6

A During the active turnover, Y244 cycles between the neutral form (YH), tyrosyl radical form (Y●) and deprotonated tyrosinate form (Y–) as depicted by the blue cycle. In all the intermediate states active in proton translocation, Y244 is in the Y– form (in red), which ensures the tight coupling of electron transfer (green arrows) and substrate proton transfer (blue arrows), via the D and K-channel into the heme a3/CuB binuclear center (BNC), to drive the proton translocation (red arrows) via the D or H channel from the N to P-side of the membrane. B The protonation of the tyrosinate to the YH form (red) in the O state disables the proton translocation upon its reduction to R.