Biosynthesis enzyme inhibitors

The proposed pathway for the biosynthesis of the avermectins (Fig. 3) has been described in a review (23). Some of the details are yet to be elucidated, although the steps, in general, are based on firm evidence from four types of studies incorporation of labeled precursors, conversion of putative intermediates by producing strains and blocked mutants, in vitro measurement of biosynthetic enzymes, and studies with enzyme inhibitors. The biosynthesis of the oleandrose units was elucidated from studies using and labeled glucose, which indicated a direct conversion of glucose to... 

The initial hydroxylation of tryptophan, rather than the decarboxylation of 5-HTP, appears to be the rate-limiting step in serotonin synthesis. Therefore, the inhibition of this reaction results in a marked depletion of the content of 5-HT in brain. The enzyme inhibitor most widely used in experiments is parachlorophenylalanine (PCPA). In vivo, PCPA irreversibly inhibits tryptophan hydroxylase, presumably by incorporating itself into the enzyme to produce an inactive protein. This results in a long-lasting reduction of 5-HT levels. Recovery of enzyme activity, and 5-HT biosynthesis, requires the synthesis of new enzyme. Marked increases in mRNA for tryptophan hydroxylase are found in the raphe nuclei 1-3 days after administration of PCPA [6]. 

Competitive inhibitors bind to specific groups in the enzyme active site to form an enzyme-inhibitor complex. The inhibitor and substrate compete for the same site, so that the substrate is prevented from binding. This is usually because the substrate and inhibitor share considerable stmctural similarity. Catalysis is diminished because a lower proportion of molecules have a bound substrate. Inhibition can be relieved by increasing the concentration of substrate. Some simple examples are shown below. Thus, sulfanilamide is an inhibitor of the enzyme that incorporates j9-aminobenzoic acid into folic acid, and has antibacterial properties by restricting folic acid biosynthesis in the bacterium (see Box 11.13). Some phenylethylamine derivatives, e.g. phenelzine, provide useful antidepressant drags by inhibiting the enzyme monoamine oxidase. The cA-isomer maleic acid is a powerful inhibitor of the enzyme that utilizes the trans-isomer fumaric acid in the Krebs cycle. 

Antimetabolites are enzyme inhibitors (see p. 96) that selectively block metabolic pathways. The majority of clinically important cytostatic drugs act on nucleotide biosynthesis. Many of these are modified nucleobases or nucleotides that competitively inhibit their target enzymes (see p. 96). Many are also incorporated into the DNA, thereby preventing replication. 

Fig. 3 Metabolic routes towards biopolyester synthesis. Dashed lines represent engineered biosynthesis routes. Triangles depict targets for inhibitors enabling biopolyester synthesis. Enzymes indicated on shaded boxes on solid lines are biopolyester biosynthesis enzymes. With kind permission from Springer Science+Business Media [7]...

The biosynthesis of the IL-12 cytokine is dependent upon various enzymes, including phosphodiesterase 4 (PDE4). Thus, PDE4 enzyme inhibitors act as functional IL-12 antagonists, and may have clinical application in the treatment of rheumatoid arthritis. 

A considerable number of enzymes occupy a central and crucial role in the activity of drugs. Dihydrofolate reductase, an enzyme involved in purine and amino acid biosynthesis, is the target of antibacterial sulfanilamides, which act both as bacteriostatics and antimalarials. These drugs act on the enzyme in different ways, some being so-called antimetabolites (i.e., reversible enzyme inhibitors). Some diuretics act on carbonic... 

Figs. 12—16 to 12—22) and prevent the progressive course of Alzheimer s disease. Direct inhibition of gene expression for the biosynthesis of these proteins is not currently possible and is currently not a very feasible therapeutic possibility. Perhaps a more realistic therapeutic possibility would be to inhibit the synthesis of beta amyloid, in much the same way that lipid-lowering agents act to inhibit the biosynthesis of cholesterol in order to prevent atherosclerosis. This could be done by means of enzyme inhibitors, such as protease inhibitors, which are at least a theoretical possibility. 

F. Whole-Cell Screening of Enzyme Inhibitors Lipid A Biosynthesis... 

JA Hoskins, RB Peery, PL Skatrud, C-yE Wu. Gene murD stem peptide biosynthesis enzyme of Streptococcus and method and kit for identification of inhibitors of MurD. U.S. Patent 5,681,694, Eli Lilly and Company, 1997. 

Structure-based design has been effectively utilized in synthesis of inhibitors of non-proteolytic enzymes. Inhibitors of MurB, an essential bacterial enzyme required for biosynthesis of peptidoglycan, were identified using the X-ray structure of the enzyme for library design. Thiazolidinone inhibitors (8) thus identified are the first examples of small molecule inhibitors of MurB. 

Lichtenthaler, H.K. (2000) Non-mevalonate isoprenoid biosynthesis enzymes, genes and inhibitors. Biochem. Soc. Trans., 28, 785-9. 

This book is one of the best known overall testaments of enzyme chemistry. It covers measurements, preparation, kinetics, nomenclature, specificity, mechanisms, inhibitors, cofactors, structures, biosynthesis, enzyme systems, and enzyme biology. In addition, a fairly broad list of classified enzymes and crystallized enzymes is appendicized. The book... 

Conclusively establishing the role of potential intermediates in a biosynthetic pathway is a difficult aspect of biosynthesis. Typically, intermediates accumulate because subsequent enzymatic reactions are slow. Organisms also produce shunt metabolites that are off the main pathway and may not be further metabolized these will also accumulate. Isolation of an intermediate does not, therefore, establish intermediacy. Trapping experiments are sometimes used to overcome these problems. In the pathway A B C, where A is a known precursor of C, labeled A and non-labeled B are fed at the same time. The latter is metabolized to C and labeled B is produced from A Bis then temporarily available for isolation. An alternative approach for microbial metabolites is to mutate the organism or add specific enzyme inhibitors. This may allow intermediates to accumulate. Incorporation of a labeled, potential intermediate into a product does not prove that the intermediate lies on the main biosynthetic pathway. It may simply serve as a substrate for the enzymes involved. Only when each of the enzymes in a pathway has been isolated and characterized, and the substrate specificity determined, can the intermediates in a biosynthetic route be characterized. 

The flavoenzyme UDP-galactop)ranose mutase (UGM) plays a key role in the cell wall biosynthesis of many pathogens, including Mycobacterium tuberculosis. McNeil and co-workers developed a microtiter plate assay for UGM (O Scheme 14) [157]. The assay is based on the release of tritiated formaldehyde from UDP-galactofuranose but not UDP-galactopyranose by periodate and was used to identify a uridine-based enzyme inhibitor from a chemical library. The potent inhibitor 320KAW73 (IC50 = 6 pM) was identified. 

Recently there has been interest in the synthesis of analogs of the naturally occurring mono- and diphosphate group. Corey and Volante ° have reported the alkylation of (dimethylphosphoryl)methyl-lithium with, for example, geranyl, famesyl and 3-methyl-2-butenyl bromides. Tlie products were assessed for their ability to inhibit the biosynthesis of squalene. McClard and coworkers described the alkylation of the phosphonylphosphinyl anion (14) to yield the P—C— P—C compounds, proven enzyme inhibitors (Scheme 13). The free acid derivatives were obtained by treatment of the alkylated products with bromotrimethylsilane. 

The sulfonamides act as competitive enzyme inhibitors and block the biosynthesis of the vitamin folic acid in bacterial cells (Fig. 10.14). They do this by inhibiting the... 

Peptide biosynthesis may occur through two different systems. Most of cellular peptides and proteins are produced by the ribosomal machinery connecting 20 proteino-genic amino acids to the desired products. However, most of the bioactive peptides are produced non-ribosomally by large peptide synthetases. These peptides are used as antibiotics, enzyme inhibitors, toxins, and other medically useful drugs. The biosynthesis of... 

Inhibitors of the bacterial cell wall biosynthesis enzyme MurD. Bioorg. Med. Chem. Lett., 8, 1643-1648. 

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