Translocation mechanism

These macromolecules include histones, ribosomal proteins and ribosomal subunits, ttansctiption factors, and mRNA molecules. The transport is bidirectional and occurs through the nucleat pote complexes (NPCs). These are complex stmctures with a mass approximately 30 times that of a ribosome and are composed of about 100 diffetent proteins. The diameter of an NPC is approximately 9 run but can increase up to ap-ptoximately 28 nm. Molecules smaller than about 40 kDa can pass through the channel of the NPC by diffusion, but special translocation mechanisms exist fot latget molecules. These mechanisms are under intensive investigation, but some important features have already emerged. 

In environments lacking a suitable external electron acceptor - such as dioxygen, sulfate, or ferric iron - respiration is not possible. Here, many organic compounds may be metabolized by fermenting microorganisms. Microbes of this class may create ATP by a direct coupling mechanism, using a process known as substrate level phosphorylation, SLP with an ion translocation mechanism like that employed by respirers, as already described or by a combination of SLP and ion translocation.1... 

Autoradiography allows the localization of radionuclide within plant tissue, which is important for an understanding of the uptake and translocation mechanisms. It also represents a selection method for the efficiency... 

Photosynthesis in all photosynthetic organisms is blocked by triazines, as well as by other PS II herbicides, when isolated thylakoid systems are tested. However, in intact plants, they express either different inhibitory potency or no inhibition. This shows that the specificity of these photosynthesis herbicides to certain weeds is not related to a difference in the chemistry of their primary target, but rather is attributed to degradative mechanisms, translocation, and translocation mechanisms. 

Krab, K. Wikstrom, M. (1987). Principles of coupling between electron transfer and proton translocation with special reference to proton-translocation mechanisms in cytochrome oxidase. Biochim. Biophys. Acta 895,25-39. 

Considering the highly processive mechanism of the protein degradation by the proteasome, a question naturally arises what is a mechanism behind such translocation rates Let us discuss one of the possible translocation mechanisms. In [52] we assume that the proteasome has a fluctuationally driven transport mechanism and we show that such a mechanism generally results in a nonmonotonous translocation rate. Since the proteasome has a symmetric structure, three ingredients are required for fluctuationally driven translocation the anisotropy of the proteasome-protein interaction potential, thermal noise in the interaction centers, and the energy input. Under the assumption that the protein potential is asymmetric and periodic, and that the energy input is modeled with a periodic force or colored noise, one can even obtain nonmonotonous translocation rates analytically [52]. Here we... 

Several details of the proton translocation mechanism have been revealed since the previous edition of this series. Thus, the proton transfer pathways have been elucidated (see above), and near consensus has been reached that all protons that... 

Figure 29.30. Translocation Mechanism. In the GTP form, EF-G binds to the EF-Tu-binding site on the 50S subunit. This stimulates GTP hydrolysis, inducing a conformational change in EF-G, and driving the stem of EF-G into the A site on the 308 subunit. To accommodate this domain, the tRNAs and mRNA move through the ribosome by a distance corresponding to one codon.

It is important to note that there are also charred linen fibrils, body-only image fibrils, blood particulates, globs, and shards occasionally present on these off-image areas. To our mind, this observation is best explained by the translocation mechanism referred to earlier. This explanation was proposed by Jackson et al. (J7) who attribute numerous foldings of the cloth as the most dominant mechanism. There appear to be at least four distinct fold patterns that are identifiable in the permanent-fold patterns that are on the Shroud. Jackson performed an experiment in which he deposited ferric oxide in locations corresponding to the blood images on the Shroud on a clean piece of cloth of the dimensions of the Shroud. After just four foldings he took sticky tape... 

Gill, D.L., Mullaney, J.M. and Ghosh, T.K. (1988). Intracellular calcium translocation mechanism of activation by guanine nucleotides and inositol phosphates. J. Exp. Biol. 139, 105-133. 

As indicated above, the number of subunits c present in Fq has been reported to be 9-12. From consideration of the model for the proton translocation mechanism, it is believed that either 9 or 12 c subunits should be present in each Fq, and that they are presumably arranged either as three trimers or three tetramers in a ring. In accord with the ratio of 3 that has been generally accepted at least up until recently for the number of protons translocated per ATP synthesized, nine protons have to be translocated during a complete catalytic cycle, since each ofthe three (a P) pairs synthesizes an ATP thus nine c-subunits are needed, one for each translocated. However, based on the recently determined ff/ATP ratio of 4 for chloroplast and cyanobacterial ATP synthasetwelve c subunits organized in three tetramers ofc subunits would be favored. 

Membrane phospholipids are synthesized on the cytoplasmic side of SER membrane. Because the polar head groups of phospholipid molecules make transport across the hydrophobic core of a membrane an unlikely event, a translocation mechanism is used to transfer phospholipids across the membrane to ensure balanced growth. Choline-containing phospholipids are found in high concentration on the lumenal side of ER membrane because a prominent phospholipid translocator protein called flippase preferentially transfers this class of molecule. 

Lanyi J K 1993 Proton translocation mechanism and energetics in the light-driven... 

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