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CA9A gene on chromosome 9p12 that encodes a carbonic anhydrase, a zinc metalloenzyme that catalyses the reversible hydration of carbon dioxide. Carbonic anhydrases participate various biological processes, including respiration, calcification, maintaining acid-base balance, bone resorption and producing aqueous humour, cerebrospinal fluid, saliva and gastric acid. CA9 is a transmembrane protein and the only known tumour-associated carbonic anhydrase isoenzyme, and may be involved in cell proliferation and transformation.
CA9 is expressed in all clear-cell type renal cell carcinomas, but is not expressed in normal kidney or most other normal organs.