OXA-58 enzyme from Acinetobacter baumannii is a carbepenm-hydrolyzing class-D β-lactamase which uses a carbamylated lysine to activate the nucleophilic serine used for β-lactam hydrolysis. The deacylating water molecule approaches the acylenzyme intermediate formed between the enzyme and the β-lactam from the α-face. According to our findings, OXA-58 uses the same catalytic machinery observed in class D β-lactamases such as OXA-10. Comparison of active site shape in OXA-58, OXA-24 and OXA-48 with the OXA-10 β-lactamase suggests that these carbapenem-hydrolyzing class D β-lactamases have gained the capability of hydrolyzing imipenem, an important carbapenem in clinical use, by slight structural changes in the active site. Also, investigation of the kinetics of β-lactam hydrolysis by Phen113A, Phen114A, Met225A, Phen113Tyr, Phen114l1e and Met225Thr shows that penicillin G is hydrolyzed better than amoxicillin and ampicillin which are hydrolyzed with comparable catalytic efficiencies. Carbenicillin was the poorest substrate.