The zinc - but not cadmium - containing ?-carbonic from the diatom Thalassiosira weissflogii is potently activated by amines and amino acids

The activation of the ?-class carbonic anhydrase (CAs, EC 4.2.1.1) from the diatom Thalassiosira weissflogii (TweCA?) incorporating both Zn(II) and Cd(II) at the active site, was investigated for the first time, using a panel of natural and non-natural amino acids and amines. CdTweCA? was completely insensitive to activation, whereas all these compounds were effective activators of the zinc-containing enzyme ZnTweCA?, with activation constants ranging between 92 nM and 37.9 µM. The most effective ZnTweCA? activators were L-adrenaline, 1-(2-aminoethyl)-piperazine and 4-(2-aminoethyl)-morpholine, with K s in the range of 92-150 nM. L-His, L- and D-Tyr and some pyridyl-alkylamines, had K s in the range of 0.62-0.98 µM, whereas L-/D-DOPA, D-Trp, histamine, serotonin and L-Asn were the next most efficient activators, with K s in the range of 1.27-3.19 µM. The least effective activators were L-Phe (K of 15.4 µM) and L-Asp (K of 37.9 µM). This in vitro study may be useful for a more complete understanding of the activation processes of various CA enzyme families, of which the ?-class was scarcely investigated.