SUBSTITUTION OF ASPARTIC ACID-217 OF CITROBACTER-FREUNDII CEPHALOSPORINASE AND PROPERTIES OF THE MUTANT ENZYMES

On the assumption that Asp-217 of a Citrobacter freundii cephalosporinase forms a salt-bridge with the conserved Lys-67, Asp-217 was changed to glutamic acid, threonine or lysine. The mutant enzymes retained about the same level of activity as that of the wild-type enzyme, and the participation of Asp-217 in the salt-bridge was ruled out. However, the mutations resulted in an increase in hydrolytic activity toward oxyimino-cephalosporins such as cefuroxime, cefmenoxime and ceftazidime, suggesting a possible mechanism of the bacterial resistance to the novel β-lactams by a single mutation in cephalosporinases. © 1990.