Proteins protein turnover

During the normal synthesis and degradation of cellular proteins (protein turnover Chapter 27), some amino acids that are released from protein breakdown and are not needed for new protein synthesis undergo oxidative degradation. 

Proteasome Large complex that degrades ubiquitin-tagged proteins Protein turnover... 

Adults also require protein in the diet. There is a continuous small loss of protein from the body, for example in hair, shed skin cells, enzymes and other proteins secreted into the gut and not completely digested. More importantly, there is turnover of tissue proteins, which are continually being broken down and replaced. Although there is no change in the total amount of protein in the body, an adult with an inadequate intake of protein will be unable to replace this loss, and will lose tissue protein. Protein turnover and requirements are discussed in Chapter 9. 

The discrepancy arises because ATP is used to drive processes which are not directly related to growth, eg membrane transport processes, protein turnover. These are called the maintenance and dissipation demands for ATP. 

However, some data have been more difficult to incorporate into the mechanism shown in Figs. 8 and 9. As reported 21) in Section II,B the Fe protein can be reduced by two electrons to the [Fe4S4]° redox state. In this state the protein is apparently capable of passing two electrons to the MoFe protein during turnover, although it is not clear whether dissociation was required between electron transfers. More critically, it has been shown that the natural reductant flavodoxin hydroquinone 107) and the artificial reductant photoexcited eosin with NADH 108) are both capable of passing electrons to the complex between the oxidized Fe protein and the reduced MoFe protein, that is, with these reductants there appears to be no necessity for the complex to dissociate. Since complex dissociation is the rate-limiting step in the Lowe-Thorneley scheme, these observations could indicate a major flaw in the scheme. 

X-ray structures of mitochondrial 6ci complexes from three different sources (113, 124, 125) have found the b- and c-type hemes at roughly identical positions, whereas the Rieske protein was seen in different places as a function of crystal space group and presence or absence of inhibitors of the enzyme. This fact was interpreted to suggest a long-range conformational movement of the Rieske protein during turnover of the complex. The range of observed positions of the Rieske protein indicated that the soluble domain can move like a... 

Lipids Proteins Undergo Turnover at Different Rates in Different Membranes... 

Several aryl esters of 6-chloromethyl-2-oxo-2//-l -benzopyran-3-carboxylic acid act as human Lon protease inhibitors (alternate substrate inhibitors)46 without having any effect on the 20S proteasome. Proteasomes are the major agents of protein turnover and the breakdown of oxidized proteins in the cytosol and nucleus of eukaryotic cells,47 whereas Lon protease seems to play a major role in the elimination of oxidatively modified proteins in the mitochondrial matrix. The coumarin derivatives are potentially useful tools for investigating the various biological roles of Lon protease without interfering with the proteasome inhibition. 

Bayot, A. Basse, N. Lee, I. Gareil, M. Pirotte, B. Bulteau, A. L. Friguet, B. Reboud-Ravaux, M. Towards the control of intracellular protein turnover mitochondrial Lon protease inhibitors versus proteasome inhibitors. Biochimie 2008, 90, 260-269. 

Newport In terms of physical limits, we tend to think of DNA, but on the other hand there is RNA degradation and protein turnover. This is how an egg is made. Even though it is only a tetraploid organism, RNA degradation is slowed down significantly, so less DNA is needed. The other physical limitation is the surface area volume relationship. How many receptors or growth factors can be inserted into a membrane ... 

Myelin components exhibit great heterogeneity of metabolic turnover. One of the novel characteristics of myelin demonstrated in early biochemical studies was that its overall rate of metabolic turnover is substantially slower than that of other neural membranes [1]. A standard type of experiment was to evaluate lipid or protein turnover by injecting rat brains with a radioactive metabolic precursor and then follow loss of radioactivity from individual components as a function of time. Structural lipid components of myelin, notably cholesterol, cerebro-side and sulfatide, as well as proteins of compact myelin, are relatively stable, with half-lives of the order of many months. One complication in interpreting these studies is that the metabolic turnover of individual myelin components is multiphasic - consisting of an initial rapid loss of radioactivity followed by a much longer slower loss. 

Steady state kinetics and protein-protein binding measurements have also been reported for the interaction of these mutant cytochromes with bovine heart cytochrome c oxidase [120]. The binding of cytochrome c variants to the oxidase occurred with increasing values of Kj in the order He (3 x 10 Mol L ) < Leu = Gly < wild-type < Tyr < Ser (3 x 10 molL ). Steady-state kinetic analysis indicated that the rate of electron transfer with cytochrome c oxidase increased in the order Ser < He < Gly < Leu < Tyr < wild-type, an order notably different from that observed for a related analysis of the oxidation of these mutants by cytochrome c peroxidase [85]. This difference in order of mutant turnover by the oxidase and peroxidase may arise from differences in the mode of interaction of the cytochrome with these two enzymes. 

Reed, S. I. Ratchets and clocks the cell cycle, ubiquitylation and protein turnover. Nat Rev Mol Cell Biol 2003,... 

VAN Nogkee, S. et al. The Multiubiquitin-Chain-Binding Protein Mcbl Is a Component of the 26S Proteasome in Saccharomyces cerevisiae and Plays a Nonessentail, Substrate-Specific Role in Protein Turnover. Mol. Cell Biol. 1996, 36, 6020-6028. 

D. M., Glickman, M., Fu, H., Coux, O., Weees, 1., Finley, D., and ViERSTRA, R. D. The multiubiquitin-chain-binding protein Mcbl is a component of the 26S proteasome in Saccharomyces cerevisiae and plays a nonessential, substrate-specific role in protein turnover. Mol. Cell. Biol. 1996, 36, 6020-6028. 

Faiola F, Liu X, Lo S, Pan S, Zhang K, Lymar E, Farina A, Martinez E. (2005) Dual regulation of c-Myc by p300 via acetylation-dependent control of Myc protein turnover and coactivation of Myc-induced transcription. Mol Cell Biol 25(23) 10220-10234... 

Different types of ACS isozymes and control of their protein turnover 101... 

The ACS of type 3 comprises many isozymes of tissue-specific activity restricted to generative organs. A majority of them have very short C-termini, making it impossible to control their protein turnover by the mechanisms described above. This feature probably proved physiologically favorable and was evolutionarily conserved. A consequence of this change is a significant decrease in the isoelectric point of type 3 ACS isozymes relative to the neutral and basic character of a majority of types 1 and 2 ACS isozymes, respectively. ... 

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