Protons functional roles

Root products are all the substances produced by roots and released into the rhizo.sphere (Table 2) (17). Although most root products are C compounds, they include ions, sometimes O, and even water. Root products may also be classified on the basis of whether they have either a perceived functional role (excretions and secretions) or a nonfunctional role (diffusates and root debris). Excretions are deemed to facilitate internal metabolism, such as respiration, while secretions are deemed to facilitate external proces.ses, such as nutrient acquisition. Both excretion and secretion require energy, and some exudates may act as either. For example, protons derived from CO2 production in respiration are deemed excretions, while those derived from an organic acid involved in nutrient acquisition are deemed secretions. 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

The extremes of these coupling strengths define two distinct functional roles for protons ... 

Ubiquinones are energy transducers that are obligatory in many respiratory and photosynthetic electron transport chains. The ubiquinone enzymes involved in these reactions usually function in a manner that couples the electron transfer by the ubiquinone to proton translocation across the membrane.The structural makeup of the ubiquinone active site permits varying functional roles that influence the electron and proton chemistry. 

Yarian CS, Basti MM, Cain RJ, Ansari G, Guenther RH, Sochacka E, Czerwinska G, Malkiewicz A, Agris PE. Structural and functional roles of the Nl- and N3-protons of P at tRNA s position 39. Nucleic Acids Res. 1999 27 3543-3549. 

The reaction takes place through the enol form of the ester function as shown in Figure S26. The electrons from the enolate add to the double bond and the resultant carbanion is quenched by a proton. The role of... 

NADH to ferricyanide, which proceeds effectively in aeorbic conditions, stops completely in anaerobic conditions. It could be supposed that in anaerobic conditions no peroxides necessary for electron transport are formed. Thus, it could be assumed that one of FMN s functions is that it maintains in mitochondrial membrane a certain optimal concentration of peroxide radicals, which are needed as catalysts of the electron transport reaction during respiration. It was shown that the formation of peroxides with the participation of FMN disappears in acid media. On the other hand, when peroxides are formed the layer adjacent to the membrane becomes enriched in protons. Hence, it follows that the peroxide formation process might possibly be a self-regulating one, the rate of which cannot rise endlessly. This circumstance once more substantiates the supposition that this process might play a very important functional role in membrane redox reactions. 

The amino acid residues E148 and Y136 have been discussed as proton sources for the initial protonation of IPP. However, E148 is likely tmprotonated under physiological conditions due to its coordination to Zn. Furthermore, site-directed mutagenesis of the conserved tyrosine in E. coli IDI-I results in a 1% residual activity, indicating a stmctural rather than a direct functional role [104, 105]. 

In addition to binding to sialic acid residues of the carbohydrate side chains of cellular proteins that the virus exploits as receptors, hemagglutinin has a second function in the infection of host cells. Viruses, bound to the plasma membrane via their membrane receptors, are taken into the cells by endocytosis. Proton pumps in the membrane of endocytic vesicles that now contain the bound viruses cause an accumulation of protons and a consequent lowering of the pH inside the vesicles. The acidic pH (below pH 6) allows hemagglutinin to fulfill its second role, namely, to act as a membrane fusogen by inducing the fusion of the viral envelope membrane with the membrane of the endosome. This expels the viral RNA into the cytoplasm, where it can begin to replicate. 

The cyanide ion plays an important role in this reaction, for it has three functions in addition to being a good nucleophile, its electron-withdrawing effect allows for the formation of the carbanion species by proton transfer, and it is a good leaving group. These features make the cyanide ion a specific catalyst for the benzoin condensation. 

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