Sensitivity bacterial enzyme

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]. 

In this chapter we describe the use of pea seeds to express the bacterial enzyme a-amylase. Bacterial exoenzymes like the heat stable a-amylase from Bacillus licheni-formis are important for starch hydrolysis in the food industry. The enzymatic properties of a-amylase are well understood [13,14], it is one of the most thermostable enzymes in nature and it is the most commonly used enzyme in biotechnological processes. Although fermentation in bacteria allows highly efficient enzyme production, plant-based synthesis allows in situ enzymatic activity to degrade endogenous reserve starch, as shown in experiments with non-crop plants performed under greenhouse conditions [12,15]. Finally, the quantitative and sensitive detection of a-amylase activ-... 

Acetaldehyde is used to hmit enzyme inhibition by trapping SO2 produced from CS A. It can be omitted if Escherichia coli AspAT is used instead of pig heart enzyme, the bacterial enzyme being less sensitive to inhibition by SO2. 

Attempts have been made to achieve colon-speeifie delivery of drugs. These include prodrugs and enteric coated polymers that are sensitive to degradation by bacterial enzymes, and matrices and hydrogels suseeptible to degradation by baeterial enzymes. 

The pharmacologic properties of parasite 7,8-dihydropteroate synthases may differ from those of the bacterial enzymes. For instance, metachloridine and 2-ethoxy-p-aminobenzoate are both ineffective against sulfonamide-sensitive bacteria, but the former has antimalarial activity and the latter is effective against infection by the chicken parasite Eimeria acervulina both activities can be reversed by p-aminobenzoate. 

Rifampicin was first shown by Hartmann et al. 54 to have a specific inhibitory effect on RNA polymerase from E. coli. Later, other active ansamycins were found and RNA polymerases from a large variety of bacteria other than E. coli proved to be sensitive to the drug. More recently, an RNA polymerase from E. coli containing only one subunit and probably involved in the initiation of DNA replication (dna G gene product) has been shown to be resistant to rifampicin5 s This holds true also for the various mammalian RNA polymerases. In contrast to non-specific inhibitors of transcription such as actinomycin and mitomycin, rifampicin interacts specifically with the bacterial enzyme itself. With the aid of 14C-labelled rifampicin it could be shown that the drug forms a very stable complex with the enzyme in a molar ratio of 1 1S6> 57 The dissociation constant of this complex is 10-9 M at 37 °C and... 

For gentamycin derivatives, the introduction of an axial hydroxymethyl substituent at C-1 in the 2-deoxystreptamine moiety reportedly ameliorates nephrotoxicity and confers protection against inactivation by bacterial enzymes. The Belgium team investigated a similar modification in the kanamycin B series [265]. As expected, l-C-(hydroxymethyl)kanamycin B (212) proved equipotent with the parent aminoglycoside (208) against kanamycin B-sensitive bacteria and the introduction of a 6"-azido, 6"-chloro, or 6"-acetamido group (213)-(215), did not reduce antibacterial activity Table 3.19). However, the introduction of a l-C-(hydroxymethyl)... 

Cdt is composed of three proteins, all encoded by the cdt operon. Two of these proteins bind to human cell membranes where they facilitate the translocation of the third subunit, a SHEP-like phosphatase PI-3,4,5-triphosphate 5-phosphatase. This bacterial phosphatase passes through the membrane and removes the 5-phosphate from PI-3,4,5-triphosphate, causing stimulated lymphocytes and macrophages to undergo apoptosis instead of growth. In nonleukocytic cells such as epidermal cells or fibroblasts, PI-3,4,5-phosphatase is exposed to PTEN, which is 10 times more active on PI-3,4,5-triphosphate than Cdt. The S I I IP-1 ike bacterial enzyme therefore cannot compete with PTEN. The sensitivity of nonleukocytic cells to Cdt is much less than that of stimulated lymphocytes and macrophages. 

One of the first important insights in the field of DNA repair was made after isolation of E. coli mutants with exceptional sensitivity to UV light [2] and subsequent mapping of mutations in genes designated uvrA, B, and C [3]. This led to the model of nucleotide excision repair [4,5]. Later the base excision repair pathway was exposed when Lindahl and coworkers [6,7] discovered a series of bacterial enzymes that recognized and removed modified nucleotides by a DNA N-glycosylase reaction. 

EPSPS has been isolated from both microorganisms and plants, and several of its properties have been studied. The bacterial and plant enzymes are mono functional with molecular mass of 44-48 kD (8-15). The fungal enzyme is a part of the multifunctional arom complex which catalyzes four other reactions of the shikimate pathway (16). While the bacterial enzymes show differences with respect to glyphosate sensitivity, the plant enzymes exhibit a much more narrow range of sensitivity (17). This accounts for the susceptibility of most plant species to glyphosate. 

The mechanism of action of rifamycins involves primarily a strong, but noncovalent, interaction with DNA-dependent RNA polymerase enzyme in sensitive bacterial cells. The mammalian enzyme is not affected, which explains the selective toxicity neither is it mutated to resistant organisms. RNA polymerase has two components. The core enzyme contains polypeptide subunits a, J3, and i and a c factor, which are needed for recognition of RNA synthesis initiation sites. The drug binds to the J subunit of the complete enzyme only. The result is effective inhibition of RNA synthesis. It is of interest that many rifampinlike hydrazine derivatives were also found to be potent inhibitors of reverse transcriptase and shown to have antiviral properties. 

Sulfonamides competitively inhibit dihydropteroate synthase, the bacterial enzyme responsible for the incorporation of ptaa-aminobenzoic acid (PABA) into dihydropteroic acid, the immediate precursor of folic acid (Figure 43—2). Sensitive microorganisms must synthesize their own folic acid, while bacteria that can use preformed folate are not affected. Mammalian cells require preformed folic acid and are not affected by sulfonamides. 

It is, however, pertinent to mention here that the mammalian dihydrofolate reductase is approximately 1 10,000 to 1 50,000 as sensitive to it as the bacterial enzymes, so that there prevails almost little interference with folate metabolism in humans. 

The mechanism of antibacterial action of the furan derivatives is unknown. However, the reduced forms of nitrofurans are highly reactive and are thought to inhibit many bacterial enzyme systems, including the oxidative decarboxylation of pyruvate to acetylcoenzyme A. Nitrofurans (see list in Table 1.7) are bacteriostatic but, at high concentrations, can be bactericidal to sensitive organisms. Both chromosomal and plasmid-mediated mechanisms of resistance to nitrofurantoin occur, and these most commonly involve the inhibition of nitrofuran reductase. 

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