title: Carbonic anhydrase C in white-skeletal-muscle tissue.
abstract: We investigated the activity of carbonic anhydrase in blood-free perfused white skeletal muscles of the rabbit. Carbonic anhydrase activities were measured in supernatants and in Triton extracts of the particulate fractions of white-skeletal-muscle homogenate by using a rapid-reaction stopped-flow apparatus equipped with a pH electrode. An average carbonic anhydrase concentration of about 0.5 microM was determined for white skeletal muscle. This concentration is about 1% of that inside the erythrocyte. Some 85% of the muscle enzyme was found in the homogenate supernatant, and only 15% appeared to be associated with membranes and organelles. White-skeletal-muscle carbonic anhydrase was characterized in terms of its Michaelis constant and catalytic-centre activity (turnover number) for CO2 and its inhibition constant towards ethoxzolamide. These properties were identical with those of the rabbit erythrocyte carbonic anhydrase C, suggesting that a type-C enzyme is present in white skeletal muscle. Affinity chromatography of muscle supernatant and of lysed erythrocytes showed that, whereas rabbit erythrocytes contain about equal amounts of carbonic anhydrase isoenzymes B and C, the B isoenzyme is practically absent from white skeletal muscle. Similarly, ethoxzolamide-inhibition curves suggested that white skeletal muscle contains no carbonic anhydrase A. It is concluded that white skeletal muscle contains essentially one carbonic anhydrase isoenzyme, the C form, most of which is probably of cytosolic origin.
mesh_terms: D000818:Animals; D002256:Carbonic Anhydrases / Q000378:metabolism; D002846:Chromatography, Affinity; D004912:Erythrocytes / Q000201:enzymology; D005016:Ethoxzolamide / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D009132:Muscles / Q000187:drug effects / Q000201:enzymology*; D011817:Rabbits; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D007527:Isoenzymes; D002256:Carbonic Anhydrases; D005016:Ethoxzolamide