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Cysteine cysteamine

The recent work by Winterbourn and Metodiewa [211] demonstrated that the above values for the rate constant of reaction of DHLA with superoxide might be overestimated. These authors studied the reactions of superoxide with several thiols, glutathione, cysteine, cysteamine, penicillamine, /V-acetylcysteine, dithiothreitol, and captopril and found that thiols reacted with superoxide by a chain mechanism with the regeneration of superoxide. They suggested that the rate constants for the reactions of thiols with superoxide could not be more than 103 ImoN1 s-1. [Pg.874]

Cysteamine (/3-mercapto-ethylamine) is used for the treatment of nephropathic cystinosis. Cysteamine converts within lysosomes cystine into cysteine and cysteine-cysteamine mixed disulfide, both of which can exit the lysosome thus removing the extra cystine. After oral administration peak plasma levels are reached at about 1.4 hours post dose. It is eliminated as a sulfate in the urine with a half-life of 4-5 hours. The most frequent adverse reactions seen involve the gastrointestinal and central nervous systems. Side effects include abdominal pain, diarrhea, drowsiness, fever, loss of appetite, nausea or vomiting and skin rash. Confusion, dizziness and headache may occur. [Pg.487]

In comparative kinetic studies we have investigated the reaction between chromate and cysteamine, mercaptoethanol and thiolactic acid, at pH 7.4 (1 M Tris HCl) and 25 °C. All the reactions appear to be first order with respect to both chromate and thiol. The second order rate constants are listed in Table 2. The rates of chromate reduction for the various monothiols follows the order cysteine > cysteamine > glutathione (fast phase) > penicillamine > mercaptoethanol > glutathione (slow phase) > thiolactic acid. [Pg.108]

We propose that at physiological pH, that the rate-determining step is the formation of the thioester from Cr(VI) and thiol. The reason for this change being twofold firstly, the Cr(VI) species HCr04 is thought to be more labile to substitution than CrOl" and there will be much less of this species at pH 7.4 (about 2% of total Cr(VI), see Sect. 2.2.1) and secondly, under conditions where HCrOl" is the dominant species, the rate of formation of the thioester is faster (about 20 times at pH 0) by a proton dependent route than by a proton independent route (see Table 4 in Ref. 51) for the reactions between chromate and cysteine, cysteamine and penicillamine. Moreover, the proton-independent rate constants for formation of the thioester in these reactions (Table 4 in Ref. 51) is of the same order of magnitude as our second order rate constants for these reactions at pH 7.4 (see Table 2). [Pg.111]

In this section we examine structurally complex thiazines, where the heterocycle forms part of a polycyclic system. Many of these fascinating natural products also contain quinone chromophores, and in many cases the corresponding compound lacking the thiazine ring also occurs in Nature. Hence it appears that the thiazine ring is added late in the biosynthetic pathway, presumably by addition of cysteine, cysteamine or hypotaurine to the quinone. [Pg.66]

Such adduct intermediates have been identified for R and R being methyl and/or the substituted aliphatic constituents of cysteine, cysteamine, and penicillamine. The same kind of intermediate also appears to be formed in the oxidation of the cysteamine thiolate, CyaS", by the disulfide radical cation of lipoic acid, Lip(SS). Identification of the adduct is based on its optical absorption ( -max ca. 380 nm, e ca. (3-4) x 10 M" cm" ) and facilitated by relatively long lifetimes (> 100 ps). In fact, the adduct formation is most appropriately formulated as a reversible process reaction (34b) ... [Pg.152]

Formation of the (RSSR) radical cations can be achieved by oxidation of disulfides with OH radicals [157, 158]. As already indicated in Section 1.1 on thiyl radicals, this reaction enters into at least two different pathways. In the case of simple aliphatic disulfides the yields of (RSSR) amount to about 50% but appear to drop for more functionalized disulfides such as cysteine, cysteamine, and others. First, these lower yields may not be the true yields since buffer effects could have distorted the time-resolved conductivity signals by which these yields have been determined. But more importantly, additional reaction pathways may be entered. For several of these compounds weak absorptions at 374 nm have been observed indicating the possible formation of perthiyl radicals [159]. This is corroborated by the fact that the decay of this presumed RSS absorption is not accelerated by OH" addition as is the case for the (RSSR) band. [Pg.185]


See other pages where Cysteine cysteamine is mentioned: [Pg.908]    [Pg.909]    [Pg.397]    [Pg.839]    [Pg.583]    [Pg.367]    [Pg.367]    [Pg.531]    [Pg.332]    [Pg.353]    [Pg.374]    [Pg.839]    [Pg.4293]    [Pg.66]    [Pg.182]    [Pg.255]    [Pg.95]    [Pg.231]    [Pg.38]    [Pg.143]    [Pg.149]    [Pg.77]   
See also in sourсe #XX -- [ Pg.346 ]




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