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Catalytic activity of human carbonic anhydrase isoform IX is displayed both extra‐ and intracellularly
Author(s) -
Klier Michael,
Jamali Somayeh,
Ames Samantha,
Schneider HansPeter,
Becker Holger M.,
Deitmer Joachim W.
Publication year - 2016
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.13562
Subject(s) - extracellular , carbonic anhydrase , intracellular , cytosol , chemistry , bicarbonate , biochemistry , intracellular ph , enzyme , microbiology and biotechnology , biology , organic chemistry
Most carbonic anhydrases catalyse the reversible conversion of carbon dioxide to protons and bicarbonate, either as soluble cytosolic enzymes, in or at intracellular organelles, or at the extracellular face of the cell membrane as membrane‐anchored proteins. Carbonic anhydrase isoform IX ( CA IX ), a membrane‐bound enzyme with catalytic activity at the extracellular membrane surface, has come to prominence in recent years because of its association with hypoxic tissue, particularly tumours, often indicating poor prognosis. We have evaluated the catalytic activity of CA IX heterologously expressed in Xenopus laevis oocytes by measuring the amplitude and rate of cytosolic pH changes as well as pH changes at the outer membrane surface ( pH s ) during addition and removal of 5% CO 2 /25 m mHCO 3 − , and by mass spectrometry. Our results indicate both extracellular and intracellular catalytic activity of CA IX . Reduced rates of CO 2 ‐dependent intracellular pH changes after knockdown of CA IX confirmed these findings in two breast cancer cell lines: MCF ‐7 and MDA ‐ MB ‐231. Our results demonstrate a new function of CA IX that may be important in the search for therapeutic cancer drugs targeting CA IX.