Translocation rate function

The protein strand can be cleaved if it lies close to the cleavage center or it could be transported forward by one amino acid. We assume that the probability of transport depends only on the length of the strand inside the proteasome. The probability of transport is, therefore, given by a translocation rate function, v(x + D) where x + D is the length of the strand inside the proteasome, in terms of amino acids. The probability of cleavage is assumed to be a constant, denoted by y. We also assume that the degradation of proteins by the proteasome is a highly processive mechanism [2], i.e., in other words, the protein is not released by the proteasome until it is completely processed. This leads to the possibility of the proteasome... 

Finally for effects where both the translocation and kinetic properties are important one can merge both models. This can be done by including the transport corrections in the kinetic model described here. In this case different transport rate functions result in different influx coefficients and, hence, different kinetic properties of the proteasome. This modeling approach is especially important for the... 

Many experimental variations are possible when performing uptake studies [246]. In a simple experiment for which the cells are initially free of internalised compound, the initial rates of transmembrane transport may be determined as a function of the bulk solution concentrations. In such an experiment, hydrophilic compounds, such as sugars, amino acids, nucleotides, organic bases and trace metals including Cd, Cu, Fe, Mn, and Zn [260-262] have been observed to follow a saturable uptake kinetics that is consistent with a transport process mediated by the formation and translocation of a membrane imbedded complex (cf. Pb uptake, Figure 6 Mn uptake, Figure 7a). Saturable kinetics is in contrast to what would be expected for a simple diffusion-mediated process (Section 6.1.1). Note, however, that although such observations are consistent... 

The two important fuels for colonocytes are glutamine and short-chain fatty acids. The oxidation of both fuels provides ATP for the cells, which is important not only to maintain digestive and absorptive functions but also to maintain membrane structure and hence the physical barrier between the lumen and the blood and peritoneal cavity. This barrier normally prevents significant rates of translocation of bacteria into the peritoneal cavity and thence into the blood. If this barrier is breached, translocation of pathogens and... 

Metabolically, radionuclides are handled in the same way as stable elements of the same atomic numher. Thus radioactive iodine simulates stable iodine, being concentrated in the thyroid gland so predictably that its rate of uptake provides an accurate measure of thyroid function. The metabolism of other radionuclides also is sufficiently characteristic so that their patterns of uptake, distribution, translocation, and excretion are similarly predictable. 

The uptake of glucose by brain, liver, kidneys, erythrocytes, and the islets of Langerhans is unaffected by insulin. However, in muscle and adipose tissues insulin stimulates glucose uptake. Part of this effect results from insulin-induced translocation of molecules of the 509-residue glucose transport protein GLUT4 (Chapter 8) from the cytosol into the plasma membrane where it can function.354-3563 Insulin apparently also increases the rate of synthesis of the transporters. 

Just as in enzyme kinetics (see chapter 7), Km here is an algebraic function of the microscopic rate constants for binding, dissociation, and translocation of the substrate in either direction. 

Meaney, S., Bodin, K., Diczfalusy, U., Bjorkhem, I. 2002. On the rate of translocation in vitro and kinetics in vivo of the major oxysterols in human circulation critical importance of the position of the oxygen function. J. Lipid Res. 43, 2130-2135. 

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