Cysteine through

A. Structure of glutathione (G-SH). [Note Glutamate is linked to cysteine through a y-carboxyl, rather than an a-carboxyl.] B. Glutathione-mediated reduction of hydrogen peroxide by NADPH. 

Clearly, there also needs to be a Group 6, Others . Tressl et al.3S2 have shown by means of model experiments that crosslinking lysine with cysteine through maleimides is possible in principle. The pathway illustrated in Scheme 8.2 was elucidated by using 4-aminobutyric acid/l-[13C]arabinose. The product readily adds thiols, such as cysteine, across the double bond under very mild conditions (pH 7, 32 °C). 

Accordingly, as the first step, the interaction of qinghaosu and cysteine in the presence of a catalytic amount of Fe(lFlll) was studied. From the reaction mixture, a water-soluble compound was isolated. This compound could be visualized with ninhydrin on TLC, and it showed a formula of C16H27NO6S H2O. Treatment of this compound with acetic anhydride yielded a cyclic thioether 165, which in turn undoubtedly showed the formation of adduct 166 of 1 and cysteine through a a bond between C-3 and sulfur. A stable adduct 167 of cysteine and 170 was then isolated in 33% yield with the same reaction protocol. As mentioned, both adducts of cysteine with primary and secondary free radical derived from arte-mether were also identified recently, albeit in low yield (Structure 5-25). More... 

The free amino acid fraction also contains 0.02-0.1% taurine (I). As such, taurine should be regarded as a major constituent of this fraction. It is obtained biosynthetically from cysteine through cysteic acid and/or from a side pathway involving cysteamine and hypotaurine (II) ... 

Many proteins contain intrinsic metal atoms that are functionally important. The most frequently used metals are iron, zinc, magnesium, and calcium. These metal atoms are mainly bound to the protein through the side chains of cysteine, histidine, aspartic acid, and glutamic acid residues. 

The isomerization of isopentenyl diphosphate to dimethylally diphos phate is catalyzed by JPP isomerase and occurs through a carbocation pathway Protonation of the IPP double bond by a hydrogen-bonded cysteine residue ir the enzyme gives a tertiary carbocation intermediate, which is deprotonated b a glutamate residue as base to yield DMAPP. X-ray structural studies on the enzyme show that it holds the substrate in an unusually deep, well-protectec pocket to shield the highly reactive carbocation from reaction with solvent 01 other external substances. 

Protected 3-methyl-D-cystein (257 Scheme 3.94), a structural unit of the peptide antibiotics nisin and subtilin, has been synthesized through the ring-opening of the aziridinecarbamide 254 with thiobenzoic acid (255) [143, 144]. The reaction took place overnight at room temperature and in methylene chloride to give 256 in greater than 95% yield. 

Cytochrome P450 monooxygenases are characterized through the presence of the heme (protoporphyrin IX) prosthetic group (Scheme 10.1) that is coordinated to the enzyme through a conserved cysteine ligand. They have obtained their name from the signature absorption band with a maximum near 450 nm in the difference spectrum when incubated with CO. The absorption arises from the Soret Jilt transition of the ferrous protoporphyrin IX-CO complex. 

More recently, miraziridine A (113) was isolated from a marine sponge related to Theonella mirabilis and shown to inhibit the cysteine protease cathepsin B. It has been shown that the aziridine ring plays a key role in this biological activity and gives rise to irreversible inhibition of cathepsins B and L, presumably through... 

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