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. 2018 Feb 28;8(1):19. doi: 10.3390/metabo8010019

Figure 2.

Figure 2

Positions and protonation states of CA IX catalytic His 200 (64 with CA II numbering) that has been implicated in proton sequestration in the acidic tumor microenvironment. (A) Deprotonated His 200 (PDB: 4Q49) in an “in” position at neutral pH = 7.5. (B) Protonated His 200 (PDB: 4Y0J) in an “out” position at acidic pH (pH = 6.0) representative of a “proton sequestered” state as in the acidic tumor microenvironment. Neutron crystallography structures of CA II were used to determine protonation states and positions and were previously determined by Fisher and McKenna [126].