BICARBONATE PROTON IN CARBONIC ANHYDRASE CATALYSIS.

Article abstract of DOI:10.1021/ja00342a056

Substitution of an alkyl group (methyl through n-pentyl) for the proton of HCO//3** minus dramatically alters the properties of the resultant alkyl carbonate esters, ROCO//2** minus , toward bovine carbonic anhydrase (BCA). While HCO//3** minus is the natural substrate of BCA, with a turnover number of approximately 10**6 s** minus **1, the alkyl carbonates show no detectable substrate activity under conditions designed to detect catalysis of substrates with turnover numbers less than 10**1 s** minus **1. The alkyl carbonates bind efficiently to BCA, however, acting as typical anionic inhibitors of BCA-catalyzed CO//2 hydration, with K//i values comparable to those of the alkyl carboxylates, RCO//2** minus , under the same conditions. The authors hypothesize the substitution of an alkyl group inhibits a proton transfer essential in the BCA-catalyzed dehydration of HCO//3** minus . It is shown that the proton of HCO//3** minus also permits a unique binding interaction with BCA.