The extracellular endonuclease of Serratia marcescens. II. Active site amino acid residues and a hypothetical mechanism of enzyme functioning

A catalytic mechanism of Serratia marcescens endonuclease [EC 3.1.4.9] is p roposed, basing on X-ray crystallographic data and functional characteristi cs of the enzyme and on the amino acid sequences of related proteins. The m echanism involves histidine and glutamic acid residues as general acid-base catalysts, as well as aspartic acid and arginine residues. Similarities an d differences between the active sites of the nuclease and pancreatic DNase I are analyzed.