NMR study of the effect of 5′-AMP on β-lactamase-catalyzed hydrolysis of penicillins

Abstract

The β-lactamase-catalyzed hydrolysis of penicillins can be followed by a novel NMR method. During the reaction, methyl proton signals of the penicillin decrease in intensity, while new methyl signals of the product, penicilloic acid, appear and increase in intensity. The half-life is easily measured as the time for the signals to be of equal intensity. With 6-aminopenicillanic acid, which is the precursor to a large number of semisynthetic penicillins, the reaction rate follows the Michaelis-Menten expression. In D 2O at pD 7.0, 29°C, the presence of 5′-AMP raises the values of both apparent V max and apparent K m . An explanation for the rise in apparent V max is that a ternary enzyme-substrate-AMP (ESA) complex is formed which reacts faster than ES. An explanation for the rise in apparent K m is that the dissociation of ESA is greater than ES. At 0.068 M, penicillin-G hydrolyzes 10 times faster than 6-aminopenicillanic acid. The rate of hydrolysis of penicillin-G is unaffected by the presence of 5′-AMP.