Carbonic anhydrase from Neisseria sicca, strain 6021 II. Properties of the purified enzyme

Abstract

1. 1.|Physical and chemical properties of carbonic anhydrase (carbonate hydrolyase, EC 4.2.1.1) purified from Neisseria sicca, strain 6021, have been investigated. Sedimentation equilibrium studies gave a molecular weight of 28 600. A molecular weight near 30 000 is also supported from the close similarity of gel filtration properties with human carbonic anhydrase B. 2. 2.|The enzyme contains 0.21% of Zn corresponding to 0.92 Zn 2+ per molecular weight of 28 600. Determination of the amino acid composition shows that the contents of tyrosine, tryptophan, and proline are considerably lower than for the mammalian enzymes. The nitrogen content and the partial specific volume, estimated from the amino acid composition of the protein, are 17,7% and 0.731 ml/g, respectively. 3. 3.|Studies of the enzymatic properties show that the enzyme is a very efficient catalyst in the CO 2 hydration reaction. In activity it resembles the highly active forms (the C type) of the mammalian carbonic anhydrases. It has a weak esterase function towards p-nitrophenyl acetate. Both activities are inhibitable with carbonic anhydrase inhibitors of the sulfonamide type. The inhibitors tested seem to associate with the bacterial enzyme with binding strengths comparable in magnitude to those found for human erythrocyte carbonic anhydrases.