Antibiotic-directed enzyme

A review describes how penicillins and cephalosporins having S-aminosulfenamine side-chains at the 6- and 7-positions, respectively, may act as P-lactamase-dependent prodrugs either as antibiotics or in antibody-directed enzyme prodmg therapy (ADEPT) in the treatment of cancer <00T5699>. 

As more and more structures of antibiotic biosynthetic enzymes become available [63], engineering the specificity of the enzymes becomes a possibility. Site-directed mutagenesis experiments, made to verify the reaction mechanisms of enzymes, have already yielded mutants with potential for application. 

Penicillins, like most antibiotics, are secondary products whose synthesis is not directly linked to growth. The enzymes that produce secondary products are normally repressed or inhibited under conditions which favour rapid growth. In the early work on penicillin, Penicillium rwtatum was grown as a floating mycelium on about 2 cm depth of liquid medium. The mycelium absorbed nutrients from the medium and penicillin was excreted into the medium. The mycelium and spent medium are readily separated. 

In this chapter, by using the examples of -lactams we have briefly examined how microbial cultures may be used to produce sufficient antibiotics to meet market demands. We have also explained how enzymes (or cells) may be used to biotransform, and thereby diversify, antibiotics. By outlining the history of penicillin production, we explained how analysis and manipulation of culture regimes may be used to enhance the yields of antibiotics (and other secondary products). These studies led to die concept of directed biosynthesis by precursor feeding. 

The anti-Pseudomonas action of norfloxacin is related to its ability to inhibit chromosome duplication in rapidly-dividing cells. Which of the following enzymes participates in bacterial DNA replication and is directly inhibited by this antibiotic ... 

Direct competition. The solid phase (a microtiter plate) is coated with an antibody specific for the antigen being assayed. The sample and enzyme-labelled antigen (antibiotic) are added. There is a competition for the antibody between the labelled and unlabelled antigen (antibiotic). Substrate is added and the color produced by the enzymatic hydrolyse is inversely proportioned to the concentration of antigen in the sample... 

Resistance of pathogenic microorganisms to beta-lactam antibiotics can result from one or a few of the mechanisms listed below inability of the drug to directly find an active site a change in PBP function, which is expressed in the reduction of affinity to the drag or inactivation of the drug by bacterial enzymes. 

There are many beta-lactamases and they can be classified differently by type of substrate, replacement of genes (chromosomes or plasmids), and place of production. A few of these enzymes directly hydrolyze penicillins (penicillinases), others hydrolyze cephalosporins (cephalosporinases), and others extend to a broad spectrum of substrates. A few bacteria have the ability to induce synthesis of beta-lactamase. Synthesis of beta-lactamase, which in a normal condition is suppressed, is induced in the presence of some beta-lactam antibiotics. 

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