Cysteine lyases

CYSTATHIONINE /3-LYASE CYSTATHIONINE /3-SYNTHASE CYSTEINE CONJUGATE /3-LYASE CYSTEINE LYASE... 

Our laboratory has studied the stereochemistry of methyl group formation in a number of a, 0 elimination reactions of amino acids catalyzed by pyridoxal phosphate enzymes. The reactions include the conversions of L-serine to pyruvate with tryptophan synthase 02 protein (78) and tryptophanase (79), of L-serine and l-tyrosine with tyrosine phenol-lyase (80), and l-cystine with S-alkylcysteine lyase (81). In the latter study, the stereospecific isotopically labeled L-cystines were obtained enzymatically by incubation of L-serines appropriately labeled in the 3-position with the enzyme O-acetyl serine sulfhy-drase (82). The serines tritiated in the 3-position were prepared enzymatically starting from [l-3H]glucose and [l-3H]mannose by a sequence of reactions of known stereochemistry (81). The cysteines were then incubated with 5-alkyl-cysteine lyase in 2H20 as outlined in Scheme 19. The pyruvate was trapped as lactate, which was oxidized with K2Cr202 to acetate for analysis. Similarly, Cheung and Walsh (71) examined the conversion of D-serine to pyruvate with... 

However, the situation is apparently, different for one subgroup among the PLP-dependent lyases extensively studied in recent.years in our laboratory on comparative lines,cf. surveys When highly purified, lyases belonging to this subtype, namely, cysteine lyase, serine sulfhydrase, cystathionine E-synthase, and E-cyanoalanine synthase (enzy-mes 1 - it Table 1 2 and obviously are species-specific... 

Dekant W, Vamvakas S, Berthold K, et al. 1986c. Bacterial P-lyase mediated cleavage and mutagenicity of cysteine conjugates derived from the nephrocarcinogenic alkenes trichloroethylene, tetrachloroethylene, and hexachlorobutadiene. Chem Biol Interact 60 31-45. 

Like the other pectate lyases, PelZ folding appears to be mainly based on p-sheet structures. Moreover, PelZ possesses only one cysteine residue and thus can not present any intramolecular disulfide bond The folding process of this protein may be different from that of... 

Yoshida Y, Y Nakano, A Amano, M Yoshimura, H Fukamachi, T Oho, Y Koga (2002) led from Streptoccus anginosus encodes a C-S lyase with a,P-elimination activity that degrades L-cysteine. Microbiology (UK) 148 3961-3970. 

Hydrogen sulfide is a well known general metabolite produced on sulfate reduction by certain bacteria. Moreover, organic forms of sulfur can give rise to HS , hence H2S in certain bacteria. Thus, cysteine desulfhydrase (EC 4.4.1.1, cystathionine y-lyase) converts L-cysteine to H2S, pyruvate, and NH3. This enzyme shows a requirement for pyridoxal phosphate and the unstable ami-noacrylic acid is an intermediate (Equation 1) in the reaction ... 

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... 

As already noted, MT has several sources such as lyase enzymes for L-methionine and S -methyl-L-cysteine. There are complex relationships between DMS, MT, and other VOSCs in the atmosphere, and in marine and terrestrial environments. The previously cited reviews should be consulted. 

Cysteine conjugates can also be degraded by the enzyme cysteine conjugate 0-lyase, which involves pyridoxal as a cofactor as shown in Figure 7.19 (26). 

FIGURE 7.19 Metabolism of a cysteine conjugate mediated by cysteine conjugate 0-lyase. 

Studies on three different iron-sulfur enzyme systems, which all require S-adenosyl methionine—lysine 2,3-aminomutase, pyruvate formate lyase and anaerobic ribonucleotide reductase—have led to the identification of SAM as a major source of free radicals in living cells. As in the dehydratases, these systems have a [4Fe-4S] centre chelated by only three cysteines with one accessible coordination site. The cluster is active only in the reduced... 

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