Enzymes phosphotransferase

Deoxykanamycin A (/ 73), in contrast to kanamydn A, is not phosphoryl-ated by 3 -0-phosphotransferase II, while the 3 -0-phosphotransferase I producing strains show resistance. Therefore, the 4 -hydroxyl group must be involved in the binding with the enzyme phosphotransferase II. By a study of the effect of the 4 -deoxygenation with neamine, l-N-HABA-neamine, ribostamycin and butirosin, it could be established that the inactivating reaction of the phosphotransferase II can only be prevented, if the 1 -amino function is substituted by an amino acid side chain (HABA). 

Bacterial resistance to aminoglycosides is mediated through bacterial enzymes (phosphotransferases, acetyl-transferases, adenyltransferases), which inactivate aminoglycosides and prevent their binding to the ribosome. Genes encoding these enzymes are frequently located on plasmids, facilitating rapid transfer of resistance to other bacteria. 

NUCLEOSIDASES AND RELATED ENZYMES - PHOSPHOTRANSFERASES WITH A PHOSPHATE GROUP AS ACCEPTOR... 

FIGURE 10.26 Glucose transport in E. coli is mediated by the PEP-dependent phosphotransferase system. Enzyme I is phosphorylated in the first step by PEP. Successive phosphoryl transfers to HPr and Enzyme III in Steps 2 and 3 are followed by transport and phosphorylation of glucose. Enzyme II is the sugar transport channel. 

Several unique features distinguish the phosphotransferase. First, phos-phoenolpyruvate is both the phosphoryl donor and the energy source for sugar transport. Second, four different proteins are required for this transport. Two of these proteins (Enzyme I and HPr) are general and are required for the phosphorylation of all PTS-transported sugars. The other two proteins (Enzyme II and Enzyme III) are specific for the particular sugar to be transported. 

T"he extraordinary ability of an enzyme to catalyze only one particular reaction is a quality known as specificity (Chapter 14). Specificity means an enzyme acts only on a specific substance, its substrate, invariably transforming it into a specific product. That is, an enzyme binds only certain compounds, and then, only a specific reaction ensues. Some enzymes show absolute specificity, catalyzing the transformation of only one specific substrate to yield a unique product. Other enzymes carry out a particular reaction but act on a class of compounds. For example, hexokinase (ATP hexose-6-phosphotransferase) will carry out the ATP-dependent phosphorylation of a number of hexoses at the 6-posi-tion, including glucose. 

The transport of each COg requires the expenditure of two high-energy phosphate bonds. The energy of these bonds is expended in the phosphorylation of pyruvate to PEP (phosphoenolpyruvate) by the plant enzyme pyruvate-Pj dikinase the products are PEP, AMP, and pyrophosphate (PPi). This represents a unique phosphotransferase reaction in that both the /3- and y-phosphates of a single ATP are used to phosphorylate the two substrates, pyruvate and Pj. The reaction mechanism involves an enzyme phosphohistidine intermediate. The y-phosphate of ATP is transferred to Pj, whereas formation of E-His-P occurs by addition of the /3-phosphate from ATP ... 

Beside AAC enzymes two different enzyme classes, nucleotidyltransferases (ANT enzymes), and phosphotransferases (APH enzymes) modify the hydroxyl groups of aminocyclitol-aminoglycoside antibiotics. 

O-phosphotransferases that modify macrolides are produced by highly macrolide resistant E. coli isolates. However, these enzymes have no clinical importance for macrolide resistance in gram-positive bacteria, and gram-negative ones are regarded as naturally resistant [2]. 

An important additional pathway is indicated in reactions I and II of Figure 47-9. This involves enzymes destined for lysosomes. Such enzymes are targeted to the lysosomes by a specific chemical marker. In reaction I, a residue of GIcNAc-1-P is added to carbon 6 of one or more specific Man residues of these enzymes. The reaction is catalyzed by a GIcNAc phosphotransferase, which uses UDP-GlcNAc as the donor and generates UMP as the other product ... 

Man 6-P receptors, located in the Golgi apparatus, bind the Man 6-P residue of these enzymes and direct them to the lysosomes. Fibroblasts from patients with I-cell disease (see below) are severely deficient in the activity of the GIcNAc phosphotransferase. 

The Enzymes II (E-IIs) of the phosphoenolpyruvate (P-enolpyruvate)-dependent phosphotransferase system (PTS) are carbohydrate transporters found only in prokaryotes. They not only transport hexoses and hexitols, but also pentitols and disaccharides. The PTS substrates are listed in Table I. The abbreviations used (as superscripts) throughout the text for these substrates are as follows Bgl, jS-gluco-side Cel, cellobiose Fru, fructose Glc, glucose Gut, glucitol Lac, lactose Man, mannose Mtl, mannitol Nag, iV-acetylglucosamine Scr, sucrose Sor, sorbose Xtl, xylitol. 

Adenylate kinase (AK) is a ubiquitous monomeric enzyme that catalyzes the interconversion of AMP, ADP, and ATP. This interconversion of the adenine nucleotides seems to be of particular importance in regulating the equilibrium of adenine nucleotides in tissues, especially in red blood cells. AK has three isozymes (AK 1,2, and 3). AK 1 is present in the cytosol of skeletal muscle, brain, and red blood cells, and AK 2 is found in the intermembrane space of mitochondria of liver, kidney, spleen, and heart. AK 3, also called GTP AMP phosphotransferase, exists in the mitochondrial matrix of liver and heart. 

AP isoenzymes can cleave associated phosphomonoester groups from a wide variety of substrates. The exact biological function of these enzymes is not well understood. They can behave in vivo in their classic phosphohydrolase role at alkaline pH, but at neutral pH AP isoenzymes can act as phosphotransferases. In this sense, suitable phosphate acceptor molecules can be utilized in solution to increase the reaction rates of AP on selected substrates. Typical phosphate acceptor additives include diethanolamine, Tris, and 2-amino-2-methyl-lpropanol. The presence of these additives in substrate buffers can dramatically increase the sensitivity of AP ELISA determinations, even when the substrate reaction is done in alkaline conditions. 

Eukaryotic ABC transport system Phosphotransferase system (PTS) Ion-coupled transport system Signal Transduction Two-component system Bacterial chemotaxis MAPK signaling pathway Second messenger signaling pathway Ligand-Receptor Interaction G-protein-coupled receptors Ion-channel-linked receptors Cytokine receptors Molecular Assembly Ribosome assembly Flagellar assembly Enzyme assembly... 

In order to analyze the effect that conformational restriction has on the antibiotic enzymatic inactivation, three different enzymes were chosen as model systems Staphylococcus aureus ANT(4 ), Mycobacterium tuberculosis AAC(2 ) and Enterococcus faecalis APH(3 ). These proteins are representative of the three main families of enzymes that modify aminoglycosides adenyltrans-ferases, acyltransferases and phosphotransferases. In addition, there is high resolution X-ray structural information available for the three enzymes in complex with several antibiotics. 

Lysosomal enzymes phosphorylation of mannose by phosphotransferase in Golgi I-cell disease... 

Genes encoding phosphotransferases confer resistance to streptomycin Genes encoding a drug-resistant dihydropteroate synthase enzyme required for folate biosynthesis confer resistance to sulfonamide Tetracycline... 

Transfer of a phosphocholine residue to the free OH group gives rise to phosphatidylcholine (lecithin enzyme l-alkyl-2-acetyl-glycerolcholine phosphotransferase 2.7.8.16). The phosphocholine residue is derived from the precursor CDP-choline (see p. 110). Phos-phatidylethanolamine is similarly formed from CDP-ethanolamine and DAG. By contrast, phosphatidylserine is derived from phosphatidylethanolamine by an exchange of the amino alcohol. Further reactions serve to interconvert the phospholipids—e.g., phosphatidylserine can be converted into phosphatidylethanolamine by decarboxylation, and the latter can then be converted into phosphatidylcholine by methylation with S-adenosyl methionine (not shown see also p. 409). The biosynthesis of phosphatidylino-sitol starts from phosphatidate rather than DAG. 

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