AmpC, also known as Beta-lactamase, is the most widespread resistance mechanism to beta-lactam antibiotics, such as the penicillins and the cephalosporins. These antibiotics have a common element in their molecular structure: a four-atom ring known as a beta-lactam. The lactamase enzyme breaks that ring open, deactivating the molecule's antibacterial properties. Recombinant E.coli beta-lactamase protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography.