{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T12:17:58Z","timestamp":1774441078876,"version":"3.50.1"},"reference-count":0,"publisher":"Wiley","issue":"2","license":[{"start":{"date-parts":[[1972,1,1]],"date-time":"1972-01-01T00:00:00Z","timestamp":63072000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["The Journal of Physiology"],"published-print":{"date-parts":[[1972,1]]},"abstract":"<jats:p>1. Details are given of an electrometric method for measuring the activity of isoenzymes of carbonic anhydrase (EC 4.2.1.1) in catalysing the hydration of carbon dioxide under different conditions at 0\u00b0 C. In the method, a measured volume of water saturated with carbon dioxide at a known partial pressure and appropriate temperature is introduced into a buffered solution. Using a sensitive electrometer and recording instrument, the subsequent change in hydrogen ion concentration is recorded as a function of time. Under the conditions of assay, the pH change induced in the presence of substrate is very small (\u0394pH &lt; 0\u00b705 units) and the period of observation need not exceed 10 sec.<\/jats:p><jats:p>2. For enzymes isolated from guinea\u2010pig tissues, it is found that the specific activity of the \u2018high activity\u2019 isoenzyme (carbonic anhydrase C, carbonic anhydrase II, HACA) is about eighteen times that of the \u2018low activity\u2019 counterpart (carbonic anhydrase B, carbonic anhydrase I, LACA) when measured at 0\u00b0 C, pH 7\u00b72, and ionic strength 0\u00b719. Under the same conditions, the <jats:italic>K<jats:sub>m<\/jats:sub><\/jats:italic> was found to be 10 m\n<jats:sc>M<\/jats:sc> for the \u2018high activity\u2019 isoenzyme and 23 m\n<jats:sc>M<\/jats:sc> for the \u2018low activity\u2019 isoenzyme. No differences were found between the equivalent kinetic parameters of the corresponding isoenzymes isolated from different tissues.<\/jats:p><jats:p>3. The isoenzymes isolated from guinea\u2010pig tissues are found to be inhibited by acetazolamide in a non\u2010competitive manner. It is also found that the \u2018high activity\u2019 isoenzyme is many times more sensitive to this inhibitor than is the \u2018low activity\u2019 isoenzyme. Evidence is presented which indicates that one acetazolamide binding site is present on each molecule of either isoenzyme.<\/jats:p><jats:p>4. While chloride ions specifically inhibit the \u2018low activity\u2019 component of guinea\u2010pig carbonic anhydrase (<jats:italic>I<\/jats:italic><jats:sub>0\u00b75<\/jats:sub> = 40 m\n<jats:sc>M<\/jats:sc>), acetate, butyrate and pyruvate inhibit both isoenzymes. Under the conditions employed, acetate and pyruvate are more strongly inhibitory to the \u2018low activity\u2019 isoenzyme than to the \u2018high activity\u2019 isoenzyme, while butyrate is more strongly inhibitory to the \u2018high activity\u2019 isoenzyme.<\/jats:p><jats:p>5. The findings are discussed with particular reference to the physiological significance of the presence of the isoenzymes in the gastro\u2010intestinal tract. Also considered are possible relationships between the distribution of the \u2018low activity\u2019 isoenzyme in these tissues and the transport and metabolism of products of fermentation occurring in the intestinal lumen.<\/jats:p>","DOI":"10.1113\/jphysiol.1972.sp009716","type":"journal-article","created":{"date-parts":[[2014,12,19]],"date-time":"2014-12-19T10:33:10Z","timestamp":1418985190000},"page":"465-478","source":"Crossref","is-referenced-by-count":19,"title":["The isoenzymes of carbonic anhydrase: kinetic properties with particular reference to the functions in the intestinal tract"],"prefix":"10.1113","volume":"220","author":[{"given":"M. J.","family":"Carter","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"D. S.","family":"Parsons","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[1972,1]]},"container-title":["The Journal of Physiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/api.wiley.com\/onlinelibrary\/tdm\/v1\/articles\/10.1113%2Fjphysiol.1972.sp009716","content-type":"unspecified","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/physoc.onlinelibrary.wiley.com\/doi\/pdf\/10.1113\/jphysiol.1972.sp009716","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,11,8]],"date-time":"2023-11-08T15:22:04Z","timestamp":1699456924000},"score":1,"resource":{"primary":{"URL":"https:\/\/physoc.onlinelibrary.wiley.com\/doi\/10.1113\/jphysiol.1972.sp009716"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1972,1]]},"references-count":0,"journal-issue":{"issue":"2","published-print":{"date-parts":[[1972,1]]}},"alternative-id":["10.1113\/jphysiol.1972.sp009716"],"URL":"https:\/\/doi.org\/10.1113\/jphysiol.1972.sp009716","archive":["Portico"],"relation":{},"ISSN":["0022-3751","1469-7793"],"issn-type":[{"value":"0022-3751","type":"print"},{"value":"1469-7793","type":"electronic"}],"subject":[],"published":{"date-parts":[[1972,1]]}}}