title: Substrate inhibition of beta-lactamases, a method for predicting enzymatic stability of cephalosporins.
abstract: Selected cephalosporins, including cefamandole, cephaloridine, cephaloglycin, and cefoxitin, were examined for their ability to inhibit the enzymatic activity of and act as substrates for beta-lactamases produced by Enterobacter cloacae and Staphylococcus aureus. Enzyme inhibition was determined by Michaelis-Menten kinetic measurements and by a spot plate assay using a chromogenic substrate (Glaxo compound 87/312). These two methods provide comparable estimates of kinetic parameters. Inhibition of beta-lactamase, as measured by these two methods, was generally found to correlate with resistance to hydrolysis and is proposed as a preliminary method of assessing susceptibility of cephalosporins to beta-lactamase hydrolysis. Four 7-alphaOCH(3), 7-alphaH cephalosporin analogue pairs were also examined. The presence of the 7-alphaOCH(3) substituent invariably resulted in reduced susceptibility to enzymatic hydrolysis, regardless of the other C7 substituent. The 7-alphaOCH(3) compounds were also better inhibitors than were their 7-alphaH analogues, with the exception that 7-alphaOCH(3) compounds having C7 adipic acid substituents were less inhibitory to the S. aureus enzyme than were the corresponding 7-alphaH analogues. Response of these two enzymes to 7-alphaOCH(3) and 7-alphaH cephalosporins suggests that beta-lactamase hydrolysis of these compounds involves attack at the alpha side of the betalactam ring.
mesh_terms: D000581:Amidohydrolases / Q000037:antagonists & inhibitors*; D002510:Cephalosporinase / Q000378:metabolism; D002511:Cephalosporins / Q000378:metabolism / Q000494:pharmacology*; D004755:Enterobacteriaceae / Q000201:enzymology; D006868:Hydrolysis; D007202:Indicators and Reagents; D013211:Staphylococcus aureus / Q000201:enzymology; D013329:Structure-Activity Relationship; D065093:beta-Lactamase Inhibitors; D047090:beta-Lactams
chemical_list: D002511:Cephalosporins; D007202:Indicators and Reagents; D065093:beta-Lactamase Inhibitors; D047090:beta-Lactams; D000581:Amidohydrolases; D002510:Cephalosporinase