NATURE OF INHIBITION OF SOME CEPHALOSPORINASES BY CARBENICILLIN

The kinetic inhibition of 6 cephalosporinases (cephalosporin amido-.beta.-lactamhydrolase, EC 3.5.2.8) [from Pseudomonas aexuginosa, Proteus morganii, Escherichia coli and Klebsiella pneumoniae] by carbenicillin was studied. In previous cases, the inhibition usually appeared to be competitive and slowly reversible. This makes it possible to measure the 2 terms of the ratio Ki [inhibition constant] = k5/k4,k4 and k5 being, respectively, the velocity constants of formation and destruction of the enzyme-inhibitor complex. A program was prepared which made it possible to obtain these constants from only 1 experiment. With ampicillin and cloxacillin, the reaction is faster and only Ki can be measured. These facts suggest that special precautions should be taken to obtain significant values for the constants governing inhibition.