Thiols, reduction

Doong R-A, H-C Chiang (2005) Transformation of carbon tetrachloride by thiol reductants in the presence of quinone compounds. Environ Sci Technol 39 7460-7468. 

Phenols are important antioxidants, with vitamin E being the most important endogenous phenolic membrane-bound antioxidant. Membrane levels of vitamin E are maintained through recycling of the vitamin E radical with ascorbate and thiol reductants. Vitamin E is a mixture of four lipid-soluble tocopherols, a-tocopherol being the most efiective radical quencher. The reaction of a-tocopherol with alkyl and alkylperoxyl radicals of methyl linoleate was recently reported. These are facile reactions that result in mixed dimer adducts (Yamauchi etal., 1993). 

For complete reduction of all disulfides in the presence of a denaturant, react for 16 hours at 0°C and 2 hours at room temperature. For partial reduction of disulfides, the reaction time may be reduced to 2 hours at 37°C, particularly for antibody thiol reduction, if only partial reduction of thiols in the hinge region is done. 

Also cellular thiol reduction of selenium oxyanions was suggested by Painter over 60 years ago and elemental Se was proposed as one of the products.153 And in fact, red, elemental selenium is often seen in Se-amended cultures of Se-resistance bacteria.154 158 Deposition of elemental Se in plants is, so far, unknown. 

Preparation of a loading buffer containing a thiol reductant (e.g., DTT) and SDS... 

The pyridazine dioxide derivative (108) was made by intramolecular nitroso compound dimerization as shown (Scheme 23). 1,2-Oxathiin 2,2-dioxides are obtained by the addition of sulfuric acid to a,(3-unsaturated ketones, e.g. (109) — (110) (66HC(21-2)774). 1,2-Dithiins are synthesized from conjugated diynes using benzyl thiol reductive debenzylation of intermediate (111) by sodium in liquid ammonia at - 70°C gives, after aerial oxidation, the 1,2-dithiin (112) (67AG(E)698). 

This disulfide-thiol reduction process when applied to phase-separated liposomes of the composition given above is illustrated in Fig. 55. 

Alkaline phosphatase can be reversibly denatured by thiol reduction in the presence of urea (88), a treatment which dissociates the dimer. Proteins purified from alkaline phosphatase-negative mutants that are antigenically related to alkaline phosphatase are readily and reversibly dissociated by acid (65). Normal alkaline phosphatase is more stable but at a lower pH, less than 3.0, it too forms monomers with release of zinc ions. However, chelating agents that remove zinc do not cause... 

The mechanism whereby this activation occurs is rather complex but is suggested to involve the following steps [13,17,31,32,33] (a) -induced conformational change in the enzyme, which (b) exposes a disulfide group to reduction by external thiol reductants, and results in (c) removal of bound ADP from the enzyme, producing (d) an enzyme which can respond to relatively low A/ZH+ in its ATP synthetic activity, and which hydrolyses ATP. 

The activation and inactivation of the membrane-bound ATPase occur also in vivo and can be demonstrated in intact chloroplasts. Here, a thiol reductant need not be added, since the photochemically reduced protein, thioredoxin, seems to fulfill this function [36]. 

The reduction of xenobiotic disulfides is believed to be extensive and can be catalysed enzymatically by GSH reductase (Waring, 1996) or thioltransferases (Wells et al., 1993), as well as chemically by exchange with GSH, thioredoxin, cysteine or other endogenous thiols. Reduction of non-cyclic disulfides results in the formation of thiols of low molecular weight that are metabolized via the various pathways described above for simple thiols. 

Wheat Rubisco was dissociated into subunits by extreme pH treatments. The separated subunits were unable to reassemble into functional holoprotein when the starting conditions were restored. Some of the separated wheat S subunits retained their ability to form functional heterologous Rubisco when mixed with L subunits from a cyanobac-terial Rubisco indicating that the failure of the assembly was caused by the properties of plant L subunits. Dissociation of Rubisco at acid pH The acid treatment resulted in precipitation of L subunits together with some undissociated holoprotein (Table 1). The L subunits dissolved partly in neutral buffer containing 1% SDS at 40°C after long incubation, and completely if thiol reductant was also added into solution. 

In the control experiment S subunits remained in solution during dissociation of Rubisco (Table 1, fraction 1), while L subunits and undissociated holoprotein precipitated. PAGE studies and the value of L/S molar ratio revealed that undissociated holoprotein dissolved when the pellet was suspended in neutral buffer (fraction 2). On the other hand, L subunits were only soluble in neutral buffer containing detergent and thiol reductant (fraction 3). 

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