By E. P. Abraham (auth.), Professor Dr. Arnold L. Demain, Ms. Nadine A. Solomon (eds.)
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Extra resources for Antibiotics: Containing the Beta-Lactam Structure
Within a certain range, the degree of deviation from coplanarity in this nitrogen could be correlated with both chemical reactivity and antibacterial activity in synthetic penems (WOODWARD 1980; GENSMANTEL et al. 1980). Another factor that was thought to increase reactivity of the f3-lactam ring to nucleophile atack was attributed to the electron withdrawing effect of sulfur at position 1. In cephalosporins, electron-negative substituents at C3 may further contribute to this effect. 3. All of the compounds shown contain the four-membered f3-lactam ring, have a carboxyl group on the carbon atom attached to the lactam nitrogen with the stereochemistry as shown.
A) Kinetics All the enzymes studied catalyze hydrolysis or transpeptidation with substrates having the general carboxyterminal structure of L-R-o-Ala-o-Ala; reaction with water gives L-R-o-Ala + o-Ala; reaction with peptides containing a free aminogroup (Y-NH2) yields L-R-o-Ala-NH-Y + o-Ala. In the presence of a p-lactam, the antibiotic may be considered a substrate analog competing with the substrate peptide for the enzyme. The kinetics of the reactions with substrate or with the p-Iactam antibiotic may both be described in the following mechanism: A) E + peptide ~ E .
The sensitivity and relative simplicity of this approach, pioneered by SPRATT (1975), has become perhaps the most important and productive line of current investigation, substantially narrowing or even bridging the gap between enzymological and physiological approaches to the mode of action of penicillin. In addition, this technique has greatly simplified and increased the sensitivity ofbiochemical efforts in purifying the penicillin sensitive enzymes from bacteria. 5. Still another direction of research involved a number of laboratories studying the effects of penicillin and other f3-lactam antibiotics on the biosynthesis of cell wall material in various strains of bacteria, using essentially in vivo or semi-in vivo labeling techniques (MIRELMAN et aL 1976; TYNECKA and WARD 1975; WARD 1974; TAKU and FAN 1976; SCHRADER and FAN 1974; ELLIOTT et aL 1975; WARD and PERKINS 1974; MIRELMAN et at.
Antibiotics: Containing the Beta-Lactam Structure by E. P. Abraham (auth.), Professor Dr. Arnold L. Demain, Ms. Nadine A. Solomon (eds.)