The roles of carbonic anhydrase in metabolism, cell growth and cancer in animals

作者：W. Richard Chegwidden, Susanna J. Dodgson, Ian M. Spencer · 发表于：Birkhäuser Basel eBooks · 年份：2000 · DOI：10.1007/978-3-0348-8446-4_16 · 被引用次数：104 · 研究领域：Enzyme function and inhibition、Polyamine Metabolism and Applications、Ion channel regulation and function

Viewed from the standpoint of chemical reactivity, CO 2 would appear to be a more appropriate substrate than bicarbonate for carboxylation reactions, since it would be more susceptible to nucleophilic attack. However, in aqueous medium, the equilibrium between dissolved CO 2 and bicarbonate is such that, at physiological pH, bicarbonate is present at some 20-fold higher concentration. Furthermore, bicarbonate probably has greater potential for binding to enzymes since it is a more polar molecule than CO 2 . It is perhaps not surprising then, that although the product of decarboxylation reactions in catabolic processes is CO 2 , several carboxylating enzymes have evolved to employ bicarbonate, not CO 2 , as their substrate. The carboxylating enzymes in animals, which are known to bind bicarbonate as substrate, are the biotin-dependent carboxylases and the carbamoyl phosphate synthetase isozymes. These enzymes bind bicarbonate, but then generally convert it either to CO 2 (biotin-dependent carboxylases) or to an activated form of CO 2 (carbamoyl phosphate synthetases). Carbonic anhydrase (CA) is perhaps alone among enzymes in being able to bind either of these substrates. (For reviews see Rubio, 1986; Knowles, 1989 and O’Leary, 1992). These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.