Cysteine precursor

The aims of inserting a thiazolidine-4-carboxylic acid (4-thiaproline, Thz, 11) residue into peptide chains are similar to those discussed for the 4-oxaproline analogue in Section 9.2.3.4.I. Thiazolidine-4-carboxylic acid (11), particularly when disubstituted at the C5 position of the proline ring, can act as a cysteine precursor and concomitantly as an amide backbone protecting group (see Section 23.2.4). Its solubilizing properties derive from its preference for the cis configuration of the Xaa-Thz bond. 169-172 ... 

Cysteine has also been shown to passivate the surface of highly fluorescent CdS bionanocrystallites. These nanocrystals have been of interest owing to their possible use as fluorescent labels and photocatalysts. Generally, the nanoparticles were formed by the addition of inorganic sulfide (Na2S) to solutions of a cadmium cysteine precursor complex. This synthetic process yielded nanocrystals of a size dimension between 2 and 4 nm in diameter. ... 

Cysteine Precursor of taurine (used in bile acid conjugation and for other functions) reducing... 

Methionine Methyl group donor for many synthetic processes cysteine precursor Phenylalanine Precursor of tyrosine via tyrosine, precursor of catecholamines, DOPA, melanin, thyroxine... 

Methionine Cysteine Creatine Glutathione Cysteine precursor (see arginine) Antioxidant Improves antioxidant status in... 

Glycine precursor Cysteine precursor Brain development... 

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

The Strecker reaction has been performed on the aldehyde 182 prepared from L-cysteine [86] (Scheme 28). The imine was formed in situ by treatment with benzylamine, then TMS cyanide was added to afford prevalently in almost quantitative yield the syn-diamine 183, which is the precursor of (-l-)-biotin 184. The syn selectivity was largely affected by the solvent, toluene being the solvent of choice. Since the aldehyde 182 is chemically and configurationally unstable, a preferred protocol for the synthesis of 183 involved the prehminary formation of the water-soluble bisulfite adduct 185 and the subsequent treatment with sodium cyanide. Although in this case the syn selectivity was lower, both diastereomers could be transformed to (-l-)-biotin. 

L-Cysteine is a precursor of the thioethanolamine portion of coenzyme A and of the taurine that conjugates with bile acids such as taurocholic acid (Chapter 26). 

PelZ is a hydrophilic protein of 420 amino acids with a short hydrophobic sequence at its N-terminal end which has Ae characteristics of the signal sequences of exported proteins. The signal peptide may be 24 amino acids long, which would corroborate wiA the usual length encountered in prokaryotes. The molecular cloning of the pelZ gene in an expression vector pT7-6 allowed for the specific 35S-cysteine-methionine raAo-labelling of PelZ in E. coli K38. We could detect, in crude extracts, the presence of a precursor and a mature form of PelZ. After cell fractionation, Ae mature form of PelZ could be localized in Ae periplasm of E. coli. So PelZ appears to be a protein exported by Ae Sec-dependent system of translocation. 

Lenthionine has the characteristic shiitake flavor. It is formed from the precursor, lentinic acid 14 by complex reactions involving a C-S lyase enzyme.30 Cyclic polysulfides occur in other Basidiomycete mushrooms (Genus Micromp-hale and Colly bid), in some red alga, and in seeds of Parkia speciosa. The latter contain lenthionine and 1,2,4-trithiolane (1,2,4-trithiacyclopentane) 17 as well as compounds with 4, 5, or 6 sulfur atoms.31 These seeds are valued in Indonesia for a unique, onion-like odor. Djenkolic acid and dichrostachinic acid S -[(2-carboxy-2-hydroxyethylsulfonyl)-methyl]cysteine are converted by a C-S lyase enzyme to cyclic polysulfides djenkolic acid yields 1,2,4-trithiolane and 1,2,4,6-tetrathiepane the latter is also formed from dichrostachinic acid.32... 

For DMS and DMTS, S-mothyl-L-cysteine sulfoxide is a precursor action of a C-S lyase enzyme yields methanesulfenic acid, CH3-S-OH, and hence methyl methanethiosulfinate, CH3-SO-S-CH3. Disproportionation reactions yield polysulfides such as DMS.56... 

Naturally occurring alliin, the major precursor to the garlic aroma, is (RcSs)-( I )-,S -allyl-[.-cysteine sulfoxide 26 (Scheme 10) with both a chiral carbon and chiral sulfur - probably the first such compound (note that sulforaphene - see earlier - was isolated more or less simultaneously with alliin). Hence there are four possible stereoisomers. The alliin level in garlic is significant 5-14 mg g 1 fresh weight. 

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