Protein phosphatases inhibitor

Protein phosphatase 1 is regulated by protein phosphatase inhibitor proteins 401... 

Whereas inhibitors 1 and 2 and NIPP1 appear to be widely distributed in mammalian tissues, including brain, DARPP-32 shows a much more restricted distribution. The protein is enriched in discrete populations of neurons in the brain, most prominently those that express Dl-dopamine receptors (see Chs 12,46 and 54). Some neuronal cell types thus appear to contain unique species of phosphatase inhibitor proteins. The critical role played by these proteins in neuronal function is illustrated below. 

Protein Folding Problem Protein Kinase Protein Kinase A Protein Kinase C Protein Kinase Inhibitors Protein Phosphatases Protein Sorting... 

A straightforward application of an Ugi reaction in natural product synthesis has been elucidated by Bauer and Armstrong [53]. These authors prepared the intermediate 9-68 in the synthesis of the complex protein phosphatase inhibitor motuporin (9-69), by using an U-4CR process starting from the acid 9-64, the aldehyde 9-65, methylamine, and the isocyanide 9-66 via 9-67. 

Surprisingly few studies have been performed with purified toxins. When added externally to the water, toxins of various origins were tested on the cope-pod Tigriopus californicus. The protein phosphatase inhibitor okadaic acid (17) from red tide dinoflagellates [22] and the neuronal depolarizing agent do-moic acid (10) from diatoms [40, 41] had different effects on the herbivores (Scheme 3). Micromolar concentrations of okadaic acid (17) acted both as toxin... 

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. 

Protease inhibitors must be present throughout the protein isolation procedure, it may be also of interest to add specific phosphatase inhibitors to the cocktail of protease inhibitors, especially when aiming at the detection of the phosphorylated form of the protein of interest. 

In a total synthesis of cdc25A protein phosphatase inhibitor dysidiolide (46) [37], substitution on an sp carbon center by vinyl cuprate was used to accom-... 

Scheme 10.7 Protein tyrosine phosphatase inhibitor assay.

Umezawa K, Kawakami M, Watanabe T. Molecular design and biological activities of protein-tyrosine phosphatase inhibitors. Pharmacol Ther 2003 99 15-24. 

Agrawal GK, Jwa NS, Rakwal R, A novel rice Oryza sativa L.) acidic PRl gene highly responsive to cut, phytohormones, and protein phosphatase inhibitors, Biochem Biophys Res Commun 274 157—165, 2000. 

Chambers TC, Zheng B, Kuo JF (1992) Regulation by phorbol ester and protein kinase C inhibitors, and by a protein phosphatase inhibitor (okadaic acid) of P-glycoprotein phosphorylation and relationship to drug accumulation in multidrug-resistant human KB cells. Mol Pharmacol 41 1008-1015... 

Sakurada K, Zheng B, Kuo JF (1992) Comparative effects of protein phosphatase inhibitors (okadaic acid and calyculin A) on human leukemia HL60, HL60/ADR and K562 cells. Biochem Biophys Res Commun 187 488-492... 

Gunasekera, S.P. McCarthy, P.J. Kelly-Borges, M. Lobkovsky, E. Clardy, J. (1996A) Dysidiolide a novel protein phosphatase inhibitor from the Caribbean sponge Dysidea etheria. J. Am. Chem. Soc., 118, 8759-60. 

In the search for novel orally active hypoglycemic agents, a team from Hoffmann-LaRoche used the readily available (see Section 10.20.9.2.3) chloromethylpyrimido[4,3-( ]-l,2,4-triazine 86 as a starting material for the synthesis of the protein tyrosine phosphatase inhibitors 87 (individual yields were not detailed), as shown in Equation (12) <2003BML2895>. 

The piperazine-substituted pyrimido[5,4-< ][l,2,4]triazine 103 undergoes selective reaction with benzylic halides to provide the benzylic piperazinyl analogues 104 <2003BML2895> as shown in Equation (15). The products are protein tyrosine phosphatase inhibitors. 

Specific inhibitor proteins for Ser/Thr phosphatases exist which can control the activity of the protein phosphatases. These inhibitors are generally subject to regulation themselves, e.g., by phosphorylation (Fig. 7.17). 

Fig. 7.17. Regulation of protein phosphatases by inhibitor proteins. The substrates of protein kinase A include protein phosphatase inhibitors that are phosphorylated by the C subunit of protein kinase A. In the phosphorylated state, the protein phosphatase inhibitors bind to the protein phosphatase and inhibit its enzyme activity...

Fig. 7.20. Regulation of glycogen-bound protein phosphatase I. Regulation of the activity of protein phosphatase I (PPI) takes place by phosphorylation of the G subunit. The G subunit is phos-phorylated at positions PI and P2, in the process of a signal chain mediated activation of protein kinase A. As a consequence of the phosphorylation, the catalytic subunit dissociates. The phosphatase activity of the free catalytic subunit is inhibited by association with a cytosohc protein phosphatase inhibitor (I), the binding of which is also controlled via a protein kinase A mediated phosphorylation. The phosphorylated G subunit can be dephosphorylated again by protein phosphatase 2A and may bind a catalytic PPI subunit once more.

Protein phosphatase I that has dissociated from glycogen may be inactivated by association with inhibitor proteins, preventing undesired dephosphorylation of proteins in the cytosol. The activity of inhibitor proteins may in turn be controlled by reversible phosphorylation. A hormone-induced activation of protein kinase A leads to phosphorylation of inhibitor protein 1 the phosphorylated form is the active form of the inhibitor. This mechanism ensures that stimulation of protein phosphorylation mediated by cAMP and protein kinase A is not weakened by an opposing dephosphorylation (Fig. 7.17). 

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