Carbonic anhydrases manganese-substituted

Manganese-Substituted a-Carbonic Anhydrase as an Enantioselective Peroxidase... 

Oxidation Reactions Catalyzed by Manganese-Substituted Carbonic Anhydrase. 52... 

CA[Mn] Manganese-substituted bovine carbonic anhydrase mixture of isozymes... 

Scheme 1 Dialysis of carbonic anhydrase against a zinc chelate (2,6-pyridinedicarboxylate) removed 90-95% of the active-site zinc. Subsequent dialysis against Mn(ll) yielded manganese-substituted carbonic anhydrase, CA[Mn]. Similar procedures yielded manganese-substituted carbonic anhydrase isoenzyme 11 (CAll[Mn]) and manganese-substituted human carbonic anhydrase isoenzyme II (hCAII[Mn])...

Adding metal ions to apo-carbonic anhydrase creates a metal-substituted carbonic anhydrase. We focused on manganese-substituted carbonic anhydrase (CA[Mn] or CAIl[Mn] for isoenzyme 11 and hCAll[Mn] for human carbonic anhydrase). 

Metal analysis showed that manganese-substituted carbonic anhydrase contained up to 80 mol% manganese and 5-10 mol% zinc. The remaining 10-15 mol% was likely apo-carbonic anhydrase since manganese binds to apo-carbonic anhydrase less tightly than zinc (pA p =< 3.4-4.0 for Mn(ll) vs. 12.0 for Zn(ll)) [39] and dissociates rapidly in the presence of zinc = 27 min at pH 6.8) [35]. The samples showed 10-15% of original hydrolytic activity toward p-nitrophenyl acetate, likely due both to the remaining zinc and to hydrolytic activity of CA[Mn], which is 7-8% of the native carbonic anhydrase [40]. 

In 2006, two groups reported the enantioselective epoxidation of olefins by manganese-substituted carbonic anhydrase [38, 46]. In the presence of bicarbonate, hydrogen peroxide, and BBS buffer, CA[Mn] also catalyzed the enantioselective... 

Table 2 Epoxidation of styrene and p-chlorostyrene by manganese-substituted carbonic anhydrases ...

In an attempt to decide between these two possibilities, Lanir et al. have investigated the relaxation rates of the exchangeable water molecules in the inner coordination sphere of the metal in manganese-substituted bovine carbonic anhydrase B. Their conclusion is that one water molecule (and not a hydroxide ion) is directly bound to the metal at high pH values while below the pKa there is no rapidly exchanging water bound to the metal ion (cf. the conclusions of Koenig and Brown based on the results of similar studies with the cobalt enzyme). 

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