Carbonic Anhydrase

Abstract

IT was shown by Henriques¹ that the rate at which carbon dioxide is evolved in the reaction H₂CO₃⇌ CO₂ + H₂O is greatly accelerated by the presence of laked blood, mere traces of which are sufficient to catalyse this reaction⁴. That this acceleration is not due to hæmoglobin was clearly demonstrated by Meldrum and Roughton^3,4 who have separated from the red blood corpuscles a now enzyme capable of catalysing both phases of the above reaction. They described this enzyme under the name of carbonic anhydrase and gave a detailed account of its properties. Their purified preparation of this enzyme was a colourless substance, very active and sensitive to KCN, H₂S and NaN₃. The amount of this enzyme-preparation was, however, very small and scarcely sufficient even to recognize it with certainty as a protein compound. In the course of our study of metallo-protein compounds⁵ present in the red blood corpuscles, we have found that the fractions of our preparations left after the complete removal of hæmocuprein had a very high content of zinc and a high carbonic anhydrase activity. By adapting our methods of purification to preparations on larger scale, such as 10 litres of blood at a time, and taking special care to increase the yield of the zinc fraction, we have obtained a highly active preparation of carbonic anhydrase. The activities of different fractions have been tested both by the manometric ‘boat’ method³ and the colorimetric method⁶. The zinc in different fractions was determined by the dithizone and by the iodometric ferricyanide methods and was also isolated as a crystalline zinc quinaldinat salt.