Enzymes bacterial

One of the most exciting discoveries related to quinone/hydroquinone chemistry is thek synthesis by biosynthetic routes (12,13). Using bacterial enzymes to convert D-glucose [50-99-7] (7) to either 1,2- or l,4-ben2enediol allows the use of renewable raw material to replace traditional petrochemicals. The promise of reduced dependence on caustic solutions and the use of transition-metal catalysts for thek synthesis are attractive in spite of the scientific and economic problems still to be solved. 

Studies on the mechanism of action of /3-lactam antibiotics have shed considerable light on how these agents kill bacteria. They also help explain qualitative differences between various agents and why there is a correlation between the reactivity of the /3-lactam and antibacterial activity. However, it is also clear that reactivity is only one factor in determining how effectively a given /3-lactam antibiotic will inactivate bacterial enzymes (82BJ(203)223). 

Compared to penicillins, cephalosporins are generally effective against a broader range of organisms and are more resistant to /3-lactamases. /3-Lactamases are bacterial enzymes that efficiently hydrolyze /3-lactam antibiotics to inactive species in which the /3-lactam bond has been cleaved. Cephalothin was the first cephalosporin to be marketed and continues... 

In the first edition of this book this chapter was entitled "Antiparallel Beta Structures" but we have had to change this because an entirely unexpected structure, the p helix, was discovered in 1993. The p helix, which is not related to the numerous antiparallel p structures discussed so far, was first seen in the bacterial enzyme pectate lyase, the stmcture of which was determined by the group of Frances Jurnak at the University of California, Riverside. Subsequently several other protein structures have been found to contain p helices, including extracellular bacterial proteinases and the bacteriophage P22 tailspike protein. 

Amides are generally poor candidates for nucleophilic attack, but penicillin is apparently an exception, and reacts with bacterial enzymes as shown below. 

Several bacterial enzymes can modify antibiotics to inactive derivatives (Table 2). 

The chromosomes of Escherichia coli and other bacteria are single, double-stranded DNA molecules with a total length of more than 1,000 pm. Relaxed DNA exists as a helical molecule, with one full turn of the helix occurring approximately every 10.4 base pairs. This molecule must undergo several folding and compaction steps to fit into an E. coli cell which is only 1-3 pm long. Despite this enormous compaction, bacterial DNA must be accessible for the bacterial enzymes that catalize DNA replication and transcription... 

Alcohol and alcohol ether sulfates are commonly considered as extremely rapid in primary biodegradation. The ester linkage in the molecule of these substances, prone to chemical hydrolysis in acid media, was considered the main reason for the rapid degradation. The hydrolysis of linear primary alcohol sulfates by bacterial enzymes is very easy and has been demonstrated in vitro. Since the direct consequence of this hydrolysis is the loss of surfactant properties, the primary biodegradation, determined by the methylene blue active substance analysis (MBAS), appears to be very rapid. However, the biodegradation of alcohol sulfates cannot be explained by this theory alone as it was proven by Hammerton in 1955 that other alcohol sulfates were highly resistant [386,387]. 

In the hver, bilirubin is made water-soluble by conjugation with two molecules of glucuronic acid and is secreted into the bile. The action of bacterial enzymes in the gut produces urobihnogen and urobihn, which are excreted in the feces and urine. 

Hayaishi O, A Kornberg (1952) Metabolism of cytosine, thymine, uracil and barbituric acid by bacterial enzymes. J Biol Chem 197 717-732. 

Cheng T-C, JJ Calomiris (1996) A cloned bacterial enzyme for nerve agent decontamination. Enz Microbiol Technol 18 597-601. 

Cheng T-C, SP Harvey, GL Chen (1996) Cloning and expression of a gene encoding a bacterial enzyme for decontamination of organophosphorus nerve agents and nucleotide sequence of the enzyme. Appl Environ Microbiol 62 1636-1641. 

Biodegradable drilling fluid formulations have been suggested. These are formulations of a polysaccharide in a concentration insufficient to permit a contaminating bacterial proliferation, namely a high-viscosity carboxymethyl-cellulose sensitive to bacterial enzymes produced by the degradation of the polysaccharide [1419]. 

We also wanted to evaluate the disassembly of our dendritic system under physiological conditions. Thus, we synthesized a self-immolative AB6 dendron 32 with water-soluble tryptophan tail units and a phenylacetamide head as a trigger (Fig. 5.26) to evaluate disassembly in aqueous conditions. The phenylacetamide is selectively cleaved by the bacterial enzyme penicillin G amidase (PGA). The trigger was designed to disassemble through azaquinone methide rearrangement and cyclic dimethylurea elimination to release a phenol intermediate that will undergo six quinone methide elimination reactions to release the tryptophan tail units. 

The antibiotic activity of certain (3-lactams depends largely on their interaction with two different groups of bacterial enzymes. (3-Lactams, like the penicillins and cephalosporins, inhibit the DD-peptidases/transpeptidases that are responsible for the final step of bacterial cell wall biosynthesis.63 Unfortunately, they are themselves destroyed by the [3-lactamases,64 which thereby provide much of the resistance to these antibiotics. Class A, C, and D [3-lactamases and DD-peptidases all have a conserved serine residue in the active site whose hydroxyl group is the primary nucleophile that attacks the substrate carbonyl. Catalysis in both cases involves a double-displacement reaction with the transient formation of an acyl-enzyme intermediate. The major distinction between [3-lactamases and their evolutionary parents the DD-peptidase residues is the lifetime of the acyl-enzyme it is short in (3-lactamases and long in the DD-peptidases.65-67... 

After absorption in the small bowel, remaining undigested food passes from the ileum through the ileocecal valve to the colon. A major role of the colon is absorption of fluid. Some of the water and sodium absorption achieved by the colon is facilitated by short-chain fatty acids (SFCAs) formed from digestion of certain dietary fibers by colonic bacterial enzymes. 

Fructooligosaccharides Polymers of fructose that reach the colon undigested and are broken down there to short-chain fatty acids by bacterial enzymes. 

While starches are commonly used, they are relatively poor viscosifiers. Acids and bacterial enzymes readily attack the acetal linkages resulting in facile depolymerization. Both formaldehyde and isothiazolones have been used as starch biocides (17). Development of improved high temperature water viscosifiers for drilling and other oil field applications is underway. For the... 

---