lowering the ph from 7 to 5 has no effect on the second-order rate constant of enzyme acylation by benzylpenicillin and n-acetylampicillin but results in a decreased rate constant of acylation by ampicillin and ac2-l-lys-d-ala-d-ala .
C0030827
benzylpenicillin
C0002680
ampicillin