Translocation reactions, primary

A) In primary translocation reactions, primary bonds are exchanged or electrons are transferred between different pairs of chemical groups. This class of reactions may be divided into two sub-classes (7) In group translocation reactions, chemical groups or electrons pass from one side of an osmotic barrier to the other . (2) In enzyme-linked solute translocation reactions, the translocation of one or more solutes through the osmotic barrier is coupled to the translocation of chemical groups or electrons otherwise than across the osmotic barrier . 

B) In secondary translocation reactions, primary bond exchanges or the transfer of electrons do not occur. This class of reactions may be divided into three sub-classes (7) In non-coupled solute translocation, or facilitated diffusion, or uniport reactions, a single solute equilibrates across an osmotic barrier. (2) In sym-coupled solute translocation, or cotransport" , or symport reactions, two solutes equilibrate across an osmotic barrier, and the translocation of one solute is coupled to the translocation of the other in the same direction, (i) In anti-coupled solute translocation, or counter-transport , or antiport reactions, two solutes equilibrate across an osmotic barrier, and the translocation of one solute is coupled to the translocation of the other in the opposite direction. 

The work done by metabolism arises from the primary bond exchanges, and hence primary translocation reactions are the means whereby the chemical bond energy (ref. 27) is transferred to osmotic potential or is expended in the maintenance of osmotic inhomogeneity. 

After damage or infection, monocytes and KCs in the area detect the damaged cells or infectious agent and respond with release of primary mediators such as TNFa, IL-1 and some IL-6. These cytokines activate the surrounding cells, that respond with a secondary, amplified release of cytokines. This second wave includes large amounts of IL-6, which induce the synthesis of acute phase proteins in hepatocytes and chemoattractants such as IL-8 and MCP-1. These events will then lead to the typical inflammatory reactions. Both IL-1 and TNFa activate the central regulatory protein of many reactions involved in immunity and inflammation, nuclear factor kappa B (NFkB). These cytokines cause dissociation of NFkB from its inhibitor IkB, which makes translocation of NFkB to the nucleus possible. In the nucleus active NFkB induces the transcription of the second wave cytokines (see also Chapter 7 for the molecular mechanisms of cytokine-mediated cell activation). 

The photoinduced chemical transformation that follows the excitation process often activates an enzyme cascade or opens an ion channel. These secondary reactions amplify the primary event of light absorption. In some mechanisms, translocation of electrons (photosynthesis, for example) or of... 

The term ion pump, synonymous with active ion-transport system, is used to refer to a protein that translocates ions across a membrane, uphill against an electrochemical potential gradient. The primary pumps do so by utilization of energy derived from various types of chemical reactions such as ATP hydrolysis, electron transfers (redox processes), and decarboxylations, or from the absorption of light (Table 1). Secondary pumps are symport and antiport systems that derive the energy for uphill movement of one species from a coupled downhill movement of another species. The electrochemical gradient driving the latter movement is often created by a primary pump. 

Heterodisulfide (CoM-S-S-HTP) reduction - coupled to primary translocation. The reaction in which ATP is synthesized during methanol reduction to CH4 could be identified with energetically competent membrane vesicles of the methanogenic strain G61. These vesicles, which are orientated more than 90% inside-out, catalyzed CH4 formation from CH3-S-C0M by reduction with H2 (Reactions 7,8) and coupled this process with the synthesis of ATP [112]. CH3-S-C0M reduction generated a ApH (inside acidic) as monitored by acridine dye quenching protonophores and ATP synthase inhibitors exerted their effects in accordance with a chemiosmotic type of ATP synthesis [113],... 

After it became clear that the reduction of CH3-S-C0M to CH4 consists of two reactions, one of these, the reduction of the heterodisulfide of CoM-S-H and H-S-HTP with H2 (Reaction 7 of Table 2), was considered to be the coupling site for ATP synthesis [14,71], Indeed, it was shown that everted vesicles of G61 also catalyzed the reduction of the heterodisulfide with H2 or with chemically reduced factor F420, F420H2, to H-S-CoM and H-S-HTP and that this reaction was coupled with the synthesis of ATP via the mechanism of electron transport phosphorylation [114-117] (Fig. 5) (i) the reduction of the heterodisulfide was associated with primary proton translocation at a ratio of up to 2H /CoM-S-S-HTP proton translocation was inhibited by protonophores rather than by DCCD (ii) reduction of the heterodisulfide was stimulated by protonophores and inhibited... 

Methyl-H MPT coenzymeM methyltransferase - coupled to primary Na translocation. Methylene-H4MPT conversion to methyl-CoM involves two reactions (Table 2) methylene-H4MPT reductase (Reaction 5) and CFl3-H4MPT H-S-CoM methyltransferase (Reaction 6). 

The following data indicate that CH3-H4MPT H-S-CoM methyltransferase is the site of primary Na translocation (see Figs. 6 and 12) (i) the enzyme has been partially purified from Methanosarcina barkeri and Methanobacterium thermoautotrophicum and found to be tightly membrane bound [69b] (ii) inverted vesicles of the methanogenic strain G61 catalyzed methyl transfer from CH3-H4MPT to H-S-CoM. This reaction was stimulated by Na ions and was coupled with the accumulation of Na" into the vesicles. Na uptake was inhibited by Na ionophores rather than by protonophores indicating primary Na translocation [168]. 

In the following subsections experiments are described which indicate that CO2 reduction to methylene-H4MPT is driven by a primary electrochemical Na potential generated by formaldehyde reduction to CH4. These experiments include (1) studies of the mode of energy transduction of the reverse reaction, the exergonic formaldehyde oxidation to CO2 and 2H2 (2) experiments on the effects of ionophores and inhibitors on CH4 formation from CO2/H2 and CH4 formation from formaldehyde/H2, and the determination of stoichiometries of primary Na" translocation. 

These conclusions have been drawn from whole-cell studies. Evidently, conclusive evidence for primary Na translocation coupled to CO2 reduction to formyl-MFR will require the purification and reconstitution of the components involved and demonstration of a direct role of Na in the reactions catalyzed by the reconstituted system. 

Primary phosphorothiosulphenamides may be acylated, and with sodium ethoxide they are converted into trialkyl phosphorothionates. Other reactions of phosphorothiosulphenamides include the loss of sulphur upon treatment with sodium, and translocation of the amino-function when treated with thiophosphoryl halides. Treatment of the acyl chloride (71) with ethyleneimine gives an amide which undergoes ready conversion into the isocyanate (72). ... 

Fig. 2. Two kinds of photosynthetic bacterial reaction centers based on the nature of binding of the cytochromes to the membrane. P is the primary electron donor T is the intermediate electron acceptor No." refers to Cyt per RC. See text for discussion. Figure adapted from PL Dutton and RC Prince (1978) Reaction center-driven cytochrome interactions in electron and proton translocation and energy coupling. In RK Clayton and WR Sistrom (eds) Photosynthetic Bacteria, p 525. Plenum Press.

Cytochrome c oxidase (COX) is the terminal enzyme in the respiratory system of most aerobic organisms and catalyzes the four electron transfer from c-type cytochromes to dioxygen (115, 116). The A-type COX enzyme has three different redox-active metal centers A mixed-valence copper pair forming the so-called Cua center, a low-spin heme-a site, and a binuclear center formed by heme-fl3 and Cub. The Cua functions as the primary electron acceptor, from which electrons are transferred via heme-a to the heme-fl3/CuB center, where O2 is reduced to water. In the B-type COX heme-u is replaced by a heme-fo center. The intramolecular electron-transfer reactions are coupled to proton translocation across the membrane in which the enzyme resides (117-123) by a mechanism that is under active investigation (119, 124—126). The resulting electrochemical proton gradient is used by ATP synthase to generate ATP. 

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