Phosphorylation of, III

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. 

Examples of proteins that are specifically phosphorylated during the cell cycle are the lamins. Hyperphosphorylation of the lamins leads to disintegration of the nuclear lamina. Myosin in actin-myosin filaments is also specifically phosphorylated during mitosis. Other M-phase-specific phosphorylations occur at transcription factor TFIIIB, leading to inhibition of transcription by RNA polymerase III. Phosphorylation of TAP proteins (see 1.4.2.3) is also involved in general inhibition of banscription. 

As morusin (3) was assumed to interact with the phorbol ester receptor, we examined whether it inhibited the activation of protein kinase C by teleocidin in vitro [73]. Fig. (9) shows that morusin (3) inhibited the phosphorylation of histone type III-S by protein kinase C dose-dependent and that 80 pmol/L morusin caused 50% inhibition. 

The mechanisms by which antitumor-promoters suppress the tumor promotion are not known, but may be due to the following effects (i) inhibition of polyamine metabolism (ii) inhibition of arachidonic acid metabolism (iii) protease inhibition (iv) induction of differentiation (v) inhibition of oncogene expression (vi) inhibition of PKC and (vii) inhibition of oxidative DNA damage [3,6,91]. The polyamine content of cells is correlated to their proliferative, and often, their neoplastic capabilities. A key enzyme in the polyamine biosynthetic pathway, ornithine decarboxylase (ODC), catalyzes the convertion of ornithine to putrescine. Phorbol ester promoters such as TPA cause increased ODC activity and accumulation of polyamines in affected tissues. Diacylglycerol activated PKC, and the potent tumor promoter, TPA, binds to, and activates PKC, in competition with diacylglycerol. PKC stimulation results in phosphorylation of regulatory proteins that affect cell proliferation. Some chemopreventive agents have inhibitory activity towards PKC. Refer to recent review articles for further discussion [3,6,91]. 

Studies have also pointed out that there is sequence specificity in DP interactions with various IFs (Fontao et al., 2003 Meng et al., 1997 Stappenbeck et al., 1993). Although the details of these studies differ, collectively they highlight the importance of the C PRD plus the last 68 residues for DP s association with keratins and the B PRD plus linker for type III IF interactions. In addition, phosphorylation of serine 2849, which is 23 residues from the DP G-terminus, impairs interactions with IFs and may be involved in regulating the size of the DP pool that is... 

The principal function of cyt. c is to form complexes through a defined interface with protein partners in our cells. This is most established for eukaryotic cytochrome c within the mitochondrial electron transport chain (ETC), a process required for carrying out the oxidative phosphorylation of ATP.4 Formation of a complex with cyt. c reductase (an electron-donor protein from complex III) and cyt. c oxidase (an electron-acceptor protein from complex IV) leads to the transfer of electrons between otherwise separated proteins. More recently cyt. c has been found to play a critical role in the process of apoptosis or programmed cell death This in turn has led to a resurgence of interest in all aspects of cyt. c research.5 Again protein-protein interactions have been shown be essential with mitochrondrial cyt. c binding to such proteins as APAF-1 to form the multi-protein species known as the apoptosome that is now thought to be a requirement for apoptosis.6,7... 

These published data prompted the authors [82] to undertake a more detailed study of the phosphorylation of isatin by the esters of P(III) acids and hydrophosphoryl compounds. At room temperature in the absence of traces of moisture isatin 49a, 1-acetylisatin 49b, and 5-bromoisatin 49c react with trialkyl phosphites and phosphonites with the formation of the unstable 1,3,2-dioxaphospholanes 87 with a pentacoordinated phosphorus atom, which isomerize in alcohol solution to the stable phosphoryl compounds 88 ... 

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