Thiol reagents

The boron trifluoride-alkyl thiol reagent combination also operates on the basis of nucleophilic attack on an oxonium ion generated by reaction of the ether with boron trifluoride.90... 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

Poling, G. W., 1976. Reactions between thiol reagents and sulphide minerals. In Flotation. 

Nimura N, Fujiwara T, Watanabe A, Sekine M, Furuchi T, et al. 2003. A novel chiral thiol reagent for automated precolumn derivatization and high-performance liquid chromatographic enantioseparation of amino acids and its application to the aspartate racemase assay. Anal Bio-chem 315 262-269. 

Coulter CV, Kelso GF, Lin TK, Smith RA, Murphy MP. Mitochondrially targeted antioxidants and thiol reagents. Free Radic Biol Med 2000 28(10) 1547-1554. 

Burns RJ, Smith RAJ, Murphy MP. Synthesis and characterization of thiobutyl-triphenylphosphonium bromide, a novel thiol reagent targeted to the mitochondrial matrix. Arch Biochem Biophys 1995 322 60-68. 

Many enzymes (and protein substrates) require free thiol residues for proper conformation and/or activity. In this case, including a thiol reagent (such as 2-mercaptoetha-nol, dithiothreitol, dithioerythritol, or cysteine) may maintain activity. 

Monoamine oxidase (MAO) (E.C. 1.4.3.4) is an enzyme found in all tissues and almost all cells, bound to the outer mitochondrial membrane. Its active site contains flavine adenine dinucleotide (FAD), which is bound to the cysteine of a -Ser-Gly-Gly-Cys-Tyr sequence. Ser and Tyr in this sequence suggest a nucleophilic environment, and histidine is necessary for the activity of the enzyme. Thiol reagents inhibit MAO. There are at least two classes of MAO binding sites, either on the same molecule or on different isozymes. They are designated as MAO-A, which is specific for 5-HT (serotonin) as a substrate, and MAO-B, which prefers phenylethylamine. Similarly, MAO inhibitors show a preference for one or the other active site, as discussed below. 

Additional information <1, 7-9, 12-17, 21> (<7> inhibitory effect of phosphonate analogues of 1,3-diphosphoglycerate, overview [49] <21> no effect by glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-phosphate, pyruvate, phosphoenolpyruvate and lactate [70] <13> double-inhibition studies, kinetics, modeling of inhibitor binding, e.g. phosphate [55] <13> enzyme is regulated by multivalent anions, overview [55] <8> no inhibition by Hg [25] <1,7,9,12-17> yeast enzyme is insensitive to thiol reagents [17]) [17, 25, 49, 55, 70]... 

Johnson and Robinson eds) Princeton Univ Press, 469 1949 Use as a thiol reagent for proteins Garel Eur J... 

Fig. 2 b. Electronmicrograph of a sectioned preparation of isolated sarcoplasmic reticulum vesicles decorated with the electron dense thiol reagent mercuri phenylazoferritin. Note the absence of ferritin particles on the internal surface of the membrane fragment in the center of the picture50 ... 

Inhibition of a staphylococcal /3-lactamase by certain dipeptides has been reported 102), but it is not clear whether the active site was directly involved. Other remotely related and unrelated compounds as well as metals have been implicated, but the results are largely inconclusive 2,9,20,44) Of the nonspecific inhibitors, the thiol reagents have been most extensively tested and usually found ineffective. This is not surprising in view of the available data on the amino acid composition of /3-lactamases (Table III) which show total absence of cysteine. However, interesting exceptions have been reported. Thiol reagents inhibit the Zn2+-dependent /3-lactamase II of B. cereus 87, 66) and the /3-lac-... 

Kone BC, Kaleta M, Gullans SR. 1988. Silver ion (Ag+)-induced increases in cell membrane potassium and sodium permeability in the renal proximal tubule Reversal by thiol reagents. J Membr Biol 102 11-19. 

DingZ, Kim S, Dorsam RT Jin J, Kunapuli SR Inactivation ofthe human P2YI2 receptor by thiol reagents requires interaction with both extracellular cysteine residues, Cysl7 and Cys270, Blood 2003 101 3908-3914. 

As shown in table 1, dried bloodstains retain EAP activity for periods as long as 15 months. Dried bloodstains were typed blind up to 4 months without difficulty but beyond that period typing became very difficult. Dried bloodstains that could be typed after 4 months were saturated and required long incubation periods in the presence of freshly prepared thiol reagents. 

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