Enzyme protein-tyrosine-phosphatase

The TS for the tyrosine phosphate hydrolysis by the enzyme protein tyrosine phosphatase (PTP1B) has been determined using a hybrid QM(PM3)/MM potential.271 The reaction was found to be dissociative in character with no P—S bond formation in the TS but extensive P—O bond lengthening. 

Other nonbrominated aromatic derivatives were isolated from Caukrpa racemosa, in particular hydrocarbons and ethers from an Indian Caukrpa racemosa, and two vanillic add derivatives, induding a rare biphenyl moiety, from an Australian Cladophora socialis. The latter two compounds are potent inhibitors of the enzyme protein tyrosine phosphatase IB (Feng et al., 2007). 

Useful serine/threonine protein phosphatase inhibitors include microcystin-LR (which inhibits protein phosphatases 1, 2A, and 2C, and related enzymes) and /1-glycerophosphate. Sodium fluoride may also be employed. Sodium orthovanadate inhibits protein tyrosine phosphatases. 

These enzymes are more closely related, in terms of their amino acid sequences, to protein tyrosine phosphatases than to protein serine-threonine phosphatases. 

N-Nitrosamines have been shown to be inhibitors of cysteine-containing enzymes. For example, dephostatin and other N-methyl-N-nitrosoanilines (1) were found to be inhibitors of the protein tyrosin phosphatases, papain and caspase [90,91]. Inhibition results from the S-nitrosation of the critical cysteine residues in the active sites of the enzymes by the nitrosamines. Compounds 6 and 7 have been found to inhibit thrombus formation in arterioles and venules of rats [92], while N-nitrosamide 9 exhibited vasodilation and mutagenicity as a result of NO release [93]. 

The extent of tyrosine phosphorylation of signal proteins is determined both by the activity of the tyrosine kinases and also the activity of tyrosine-specific protein phosphatases. If the total activity of both enzymes in the cell is considered, it is found that there is a preponderance of protein tyrosine phosphatase activity compared to tyrosine kinase activity. In contrast, the activities of the Ser/Thr-specific protein kinases and protein phosphatases are approximately balanced. It is estimated that the activity of the protein tyrosine phosphatases is about 3-4 orders of magnitude higher than the activity of the protein tyrosine kinases. With this relationship between the activities, it is not surprising that the net level of tyrosine phosphorylation in the cell is very low and that tyrosine phosphorylation is often only transient. Consequently, it took a relatively long time until the importance of tyrosine phosphorylation for signal transduction was assessed correctly. 

Fischer, E.H., Charbonneau, H. and Tonks, N.K. Protein tyrosine phosphatases a diverse famUiy of intraceUnlar and transmembrane enzymes Sdence (1991) 253, 401-406... 

The protein tyrosine phosphatases also exist as several families with numerous functions in control of transcription, growth, differentiation, and metabolism.741-743 These enzymes function by a doubledisplacement mechanism, as in Eq. 12-38, but with a cysteine side chain rather than serine. The cysteine is present in the conserved sequence (H/V)CX5R(S/T). The arginine binds the phospho group and helps to stabilize the transition state, which probably is metaphosphate-like.742... 

A variant of Tethering with extenders, termed breakaway Tethering, has been developed for enzymes with catalytic sites that do not tolerate the insertion of a cysteine residue due to disruption of structural or functional integrity. Protein tyrosine phosphatases (PTPs)... 

Many peroxovanadates have potent insulin-mimetic properties [1,2]. Apparently, this functionality derives from the ability of these compounds to rapidly oxidize the active site thiols found in the group of protein tyrosine phosphatases that are involved in regulating the insulin receptor function [3], The discovery of vanadium-dependent haloperoxidases in marine algae and terrestrial lichens provided an additional stimulus in research toward obtaining functional models of peroxidase activity, and there is great interest in duplicating the function of these enzymes (see Section 10.4.2). 

Another AT2 pathway linked to apoptosis leads to a stimulation of a soluble protein tyrosine phosphatase, SHP-1, an enzyme that associates with insulin receptor substrate (IRS)-2 (Cui et al. 2002). Overexpression of a dominant negative form of SHP-1 in PC12W cells has been found to attenuate AT2 receptor-mediated inhibition of insulin signaling. Since insulin activates Akt, it is interesting that the mechanism of apoptosis in the angiotensin II-treated PC12W cell involves the dephosphorylation and inactivation of Akt. In NIE-115 neuroblastoma cells,... 

As an example of this technology, a library of 125 cinnamate capped tripeptides was synthesized on Rink resin [17] using five amino acid building blocks per coupling step (Scheme 5) [ 16], This library was screened against the human protein tyrosine phosphatase PTP1B enzyme and a number of potent inhibitors were identified (40 nMtechnique based on microchips to which information is written before each chemical step [18],... 

Reversible chemical modification of enzymes, which was discovered in 1955 by Edmond Fischer and Edwin Krebs [58], is a more prevalent mechanism for cellular signaling switching. Fischer and Krebs showed that enzymes can be turned from an inactive form to an active form via phosphorylation of certain residues of the protein. Enzymes that catalyze phosphorylation (addition of a phosphate group coupled with ATP or GTP hydrolysis) are called protein kinases. Enzymes that catalyze dephosphorylation (which is not the reverse reaction of the phosphorylation) are called phosphatases. For example, a protein tyrosine phosphatase is an enzyme that catalyzes the removal of a phosphate group from a tyrosine residue in a phosphorylated protein [57],... 

E. H. Fischer, H. Charbonneau, and N. K. Tonks. Protein tyrosine phosphatases a diverse family of intracellular and transmembrane enzymes. Science, 253 401-406, 1991. 

The best-studied protein tyrosine phosphatases are the high molecular weight cytoplasmic enzymes of the FTP family. X-ray structures of the human FTP IB cytosolic tyrosine phosphatase, have been solved by David Barford et and that of a Yersinia tyrosine phosphatase by Fauman et In Fig. 3.9a and b the structures of the... 

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