title: Role of zinc in catalytic activity of carbonic anhydrase IX.
abstract: The carbonic anhydrases (CAs) in the α class are zinc-dependent metalloenzymes. Previous studies have reported that recombinant forms of carbonic anhydrase IX (CAIX), a membrane-bound form of CA expressed in solid tumors, appear to be activated by low levels of zinc independent of its well-studied role at the catalytic site. In this study, we sought to determine if CAIX is stimulated by zinc in its native environment. MDA-MB-231 breast cancer cells express CAIX in response to hypoxia. We compared CAIX activity associated with membrane ghosts isolated from hypoxic cells with that in intact hypoxic cells. We measured CA activity directly using (18)O exchange from (13)CO(2) into water determined by membrane inlet mass spectrometry. In membrane ghosts, there was little effect of zinc at low concentrations on CAIX activity, although at high concentration zinc was inhibitory. In intact cells, zinc had no significant effect on CAIX activity. This suggests that there is an appreciable decrease in sensitivity to zinc when CAIX is in its natural membrane milieu compared to the purified forms.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Chingkuang
authors.initials: C
authors.lastname: Tu
authors.forename: Lauren
authors.initials: L
authors.lastname: Foster
authors.forename: Andrea
authors.initials: A
authors.lastname: Alvarado
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
authors.forename: David N
authors.initials: DN
authors.lastname: Silverman
authors.forename: Susan C
authors.initials: SC
authors.lastname: Frost
mesh_terms: D000951:Antigens, Neoplasm / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002384:Catalysis; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology; D005260:Female; D006801:Humans; D007700:Kinetics; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000951:Antigens, Neoplasm; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D015032:Zinc