Cysteine function

However, if paracetamol is taken in overdose, the levels of quinoneimine exceed the ability of glutathione to convert it back to paracetamol and toxicity to the liver results. In some cases, if treatment is not initiated in time, severe toxicity results, leading to death by acute liver failure. Treatment of paracetamol overdose is by administration of N-acetylcysteine (Figure 5.8). This compound (the acetyl derivative of the essential amino acid cysteine) functions as an alternative source of thiol (—SH) groups, which act in a similar manner to glutathione to detoxify the quinoneimine. 

Characteristic features of c-type cytochromes include an axial histidine, an axial methionine (bodi coordinated to the iron centre) and two diioedier linkages between the porphyrin and cysteine functions of the protein. 

A soln. of N-rcrr-butoxycarbonyl-S"[(N -methyl-N -phenylcarbamyl)]sulfenyl-L-cysteine in CDCI3 treated with 0.05 M dithiothreitol and 0.01 MN-methylmorpholine for a few min (half-life ca. 16 min)- N-ter/-butoxycarbonyl-L-cysteine. Y 100%. The protected cysteine function appears to have promise for the step-wise incorporation of the aminoacid residue into cysteinyl-containing peptides by standard solid-phase synthesis the carbamyldisulfide is highly acid-stable (to anhydrous HF, CF3SO3H). F. method s. A.L. Schroll, G. Barany, J. Org. Chem. 54, 244-7 (1989). 

Rapid and sensitive colorimetric sensor for the detection of Hg using L-cysteine-functionalized GNPs induced by ultraviolet radiation The L-cysteine-modified GNPs aggregate quickly in the presence of Hg. Functionalized GNPs can be used for delivery of various payloads into cells, such as small drug molecules or laige biomolecules like DNA and siRNA Chai et al. [61]... 

Chai F, Wang C, Wang T, Ma Z, Su Z (2010) L-cysteine functionalized GNPs for the colorimetric detection of Hg" induced by ultraviolet light. Nanotechnology 21 025501... 

The thiol group is found in the amino acid L-cysteine. L-Cysteme is important because the thiol groups of pairs of cysteines are oxidized to disulfide bonds (Section 10.9G), which are a major factor in stabilizing the three-dimensional structure of protein molecules. The thiol group of cysteine functions as a nucleophile in certain enzyme mechanisms. In addition, it binds the metal in certain metal-containing enzymes. 

Fig. 1 Schematic illustration of the various coupling methods that have been developed in order to post-functionalize liposomes, a Amine functionalization, b carboxylic acid functionalization, c aldehyde functionalization, d hydrazine functionalization, e maleimide ftmctionalization, f thiol functionalization, g thiol functionalization (disulfide bond formation), h bromoacetyl functionalization, i cysteine functionalization, j cyanur functionalization, kp-nitrophenylcarbonyl functionalization, I alkyne functionalization, m triphosphine functionalization...

Functionalized micelles are increasingly being studied. An L-cysteine-functional-ized cationic micelle (27) is 1860-fold more effective than micelles of hexadecyl-trimethylammonium chloride in cleaving 4-nitrophenyl acetate. Acetylation of the thiol group occurs, followed by an intramolecular S- N transfer leaving the thiol group to cleave another molecule of the ester. ... 

R. A. Moss, R. G. Mahas, and T. L. Lukas (1978), A cysteine-functionalized micellar catalyst. Tetrahedron Lett. 507-510. 

---