A protein inhibitors

Bash P A, U C Singh, F K Brown, R Langridge and P A Kollman 1987. Calculation of the Relat Change in Binding Free-Energy of a Protein-Inhibitor Complex. Science 235 574-576. 

Both phosphorylase a and phosphorylase kinase a are dephosphorylated and inactivated by protein phos-phatase-1. Protein phosphatase-1 is inhibited by a protein, inhibitor-1, which is active only after it has been phosphorylated by cAMP-dependent protein kinase. Thus, cAMP controls both the activation and inactivation of phosphorylase (Figure 18-6). Insulin reinforces this effect by inhibiting the activation of phosphorylase b. It does this indirectly by increasing uptake of glucose, leading to increased formation of glucose 6-phosphate, which is an inhibitor of phosphorylase kinase. 

Bash, P. A. Singh, U. C. Brown, F. K. Langridge, R. Kollman, P. A., Calculation of the relative change in binding free energy of a protein-inhibitor complex, Science 1987, 235, 574-576... 

In ischemic (oxygen-deprived) cells, a protein inhibitor blocks ATP hydrolysis by the ATP synthase operating in reverse, preventing a drastic drop in [ATP]. 

Cooperative binding of the synthetic substrate bis(p-nitrophenyl) phosphate and of a protein inhibitor (see Sections III,D,2 and 3) might also be considered as an indirect indication of a dimeric structure. 

A protein inhibitor has been extracted and partially purified from mouse liver by Lesca and Paoletti 45). This protein inhibits acid DNases from different tissues and species but not pancreatic or E. coli DNases. Very interestingly, V vs. substrate concentration plots become sigmoid in the presence of the inhibitor provided that pH is lower than 5.6. The existence of a DNase-inhibitor complex is suggested by sucrose-gradient results. An unusual feature of the inhibitor is its ability to reactivate acid DNase preparations treated with 8 M urea. 

A. D. Rowan, J. Brain, D. J, Buttle, and A. J. Barrett Inhibition of cysteine proteinasea by a protein inhibitor from potato. FEBS Lett. 269 326 (1990). 

Miller, C., Moczydlowski, E., Latorre, R., and Phillips, M. 1985. Charybdotoxin, a protein inhibitor of single Ca2+-activated K+ channels from mammalian skeletal muscle. Nature 313 316-318. 

STD-NMR cannot readily distinguish between specific and nonspecific binding events. Therefore, an extension of STD-NMR involves the titration of a protein-inhibitor complex with a test ligand that will compete with the inhibitor in fast exchange for the same receptor-binding site on the protein. This situation... 

A protein inhibitor of cyclic AMP-activated protein kinase has been isolated from mammalian tissue and this promotes a five-fold increase in the binding constant of cyclic AMP to protein kinase [79]. The inhibitor is assumed to interact with the catalytic subunit at the regulatory subunit binding site. Thus, inhibitor protein and regulatory subunit modulate the catalytic subunit activity by an identical mechanism. However, it may be more complex, as a protein kinase modulator protein has been isolated which alters the substrate specificity both of cyclic AMP and of cyclic GMP-activated protein kinases, increasing the phosphorylation of some protein substrates and decreasing that of others [80]. 

Fig. 7.3. Evolution of the biochemical parameters of the mechanism of intercellular communication during the hours that follow starvation in D. discoideum. The variation in the activity of (a) adenylate cyclase and (b) intra- and extracellular phosphodiesterase and (c) the evolution of the quantity of cAMP receptor measured in experiments performed with two different levels of cAMP. In (b), circles and triangles refer to total phosphodiesterase and to a protein inhibitor of the enzyme, respectively closed symbols relate to cells treated by pulses of cAMP resulting in 10" M cAMP every 5 min, whereas open symbols relate to untreated cells (data collected from various authors by Loomis, 1979).

Calcularion of e Relative Change in Binding Free Energy of a Protein-Inhibitor Complex. 

The endogenous level of cAMP can be regulated either by activation of adenyl cyclase as described, which leads to stimulation of cAMP synthesis, or by degradation of cAMP by a phosphodiesterase, which is specific for one of the phosphate ester bonds in the molecule. The activity of the phosphodiesterase is, in turn, also subject to regulation. Thus, for example, a protein inhibitor of the phosphodiesterase has been detected in slime molds (Acrasiales). In some Acrasiales such as Dictyostelium dis-coideum cAMP is identical with acrasin, a chemotactic substance which plays an important role in the aggregation of the myxamoeba to pseudoplasmodia. 

The first key intermediate in the synthesis of Anacetrapib (MK-0859) a protein inhibitor has been synthesized at a kilogram scale via controlled monoarylation with ruthenium(Il) catalyst of a phenyloxazoline derivative with a fluorinated arylbromide [(Eq. 22)] [92]. This successful catalytic reaction was due to the combination of [RuCl2(benzene)]2 with 10 KOAc in the presence of K3PO4. The further addition of 1 equiv. of PPha per Ru atom favoured the oxidative addition of ArBr to the ruthenacycle intermediate and also decreased the diarylation rate. 

It appears that a protein inhibitor termed "hemin controlled repressor" (HCR) forms in hemin-deficient cells from a latent "prorepressor." This inhibitor appears to function as a protein kinase, adding one to two phosphorus atoms to the small subunit of eIF-2. Whether this activity is cAMP dependent (Datta et al., 1978) or not (Gross, 1978 Safer and Anderson, 1978) has not been resolved. The effect of the HCR appears to be to decrease the amount of initiator Met-tRNAf which binds to the 40 S subunit. The ability of eIF-2 to counteract the effect of HCR, in conjunction with the data on phosphorylation, strongly supports a role for HCR as inhibitor of the action of eIF-2. However, the actual means by which phosphorylation of the initiator factor leads to inhibition, or how hemin works, is not clear. Clarification of this phenomenon should prove illuminating not only for hemoglobin synthesis but also for nonerythroid cells, since the effect of hemin is seen with extracts from other cells as well. 

Hayashi S, Murakami Y, Matsufuji S (1996) Ornithine decarboxylase antizyme a novel type of regulatory protein. Trends Biochem Sci 21 27-30 Heller JS, Fong WF, CaneUakis ES (1976) Induction of a protein inhibitor to ornithine decaibox-ylase by the end products of its reaction. Proc Natl Acad Sci USA 73 1858-1862 Howard MT, Shirts BH, Zhou J, Carlson CL, Matsufuji S, Gesteland RE, Weeks RS, Atkins JE (2001) CeU culture analysis of the regulatory frameshift event required for the expression of mammalian antizymes. Genes Cells 6 931-941... 

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