L-Cysteine desulfhydrase

L-Cysteine desulfhydrase in leaves of cucurbit plants is a constitutive enzyme whose activity can be enhanced by preincubation of leaf discs with L-cysteine, D-cysteine, or structural analogs of L-cysteine at millimolar concentrations preincubation with cystine does not affect the activity of the enzyme (20.261. Although the stimulation of L-cysteine desulfhydrase activity is... 

PLP-dependent desulfhydrases necessarily show very similar mechanisms, but often come from independent evolutionary lineages. For example, although most bacterial L-cysteine desulfhydrases are fold-type I enzymes belonging to the same evolutionary branch as cystathionine f3- and 7-lyases, L-cysteine desulfhydrase from Fusobacterium nucleatum is a member of the fold-type II group and its closest sequence homologue is a cysteine synthase. D-cysteine desulfhydrase from E. coli is also a fold-type II enzyme not strictly related to other desulfhydrases but resembling instead an ACC deaminase. ... 

Since even a slightly elevated L-cysteine concentration is inhibitory or possibly toxic for the cells E. coli possesses another mechanism for detoxification of this compound in addition to excretion degradation of L-cysteine. Five enzymes with L-cysteine desulfhydrase activity have been identified so far in this organism L-tryptophanase (TnaA), L-cystathionine p-lyase (MetC),... 

O-acetyl-L-serine (thiol)-lyase A (CysK), O-acetyl-L-serine (thiol)-lyase B (CysM) and MalY. Thus in order to engineer a potent L-cysteine over-producer excessive degradation of the amino acid must be prevented by inactivation of the genes encoding the major L-cysteine desulfhydrase activities. 

If L-cysteine desulfhydrase is responsible for the H2S emitted by plants in the presence of L-cysteine, the lower rates of H2S evolution obtained with D-cysteine seem anomalous in view of the much higher activity of the D-specific enzyme in the tissues examined. At least part of this apparent anomaly can be attributed to the more rapid uptake of the L-isomer, which is about fourfold greater than with D-cysteine. Although L-cysteine desulfhydrase has not been purified and the kinetics examined in detail, the available information suggests... 

L-cysteine (derivatives) /5-chloro-DL-alanine + Na2S Cys desulfhydrase Enterobactor cloacae 193... 

The enantiomers of this drug differ in their efficacy and activity, with (D)-penicilla-mine being the enantiomer required for pharmaceutical preparations. The (l)-enantiomer is toxic, and its absorption by the human body is more than the (D)-enantiomer. While both enantiomers of penicillamine are desulfhydrated by (r.)-cysteine desulfhydrase, only the (l)-isomer inhibits the action of this enzyme [2], The reported optical rotation values for (D)-penicillamine are ... 

Peak concentrations in the blood are obtained between 1 and 3 h after administration. Unlike cysteine (its nonmethylated parent compound), penicillamine is somewhat resistant to attack by cysteine desulfhydrase or L-amino acid oxidase. As a result, penicillamine is relatively stable in vivo [7,2],... 

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 ... 

L-/D-cvsteine. Hydrogen sulfide is produced from L-cysteine in a light-independent process that can be inhibited in vivo and in vitro by aminooxy acetic acid, an inhibitor of pyridoxal phosphate-dependent enzymes the hydrogen sulfide emitted in response to L-cysteine is directly derived from die L-cysteine fed ( 2 ). Therefore, hydrogen sulfide appears to be produced from L-cysteine by a pyridoxal phosphate-dependent, L-cysteine specific cysteine desulfhydrase. This conclusion is supported by the finding that in cucurbit... 

S-Substituted L-cysteines Cysteine desulfhydrase Tryptophan synthase... 

There is a general requirement for pyridoxal-5-phosphate (24, 25, 27, 44) although not all of the activity lost on dialysis is restored by adding the cofactor. This requirement explains the inhibition by hydroxylamine and hydrazine (24, 25). The reaction is a typical pyridoxal-5-phosphate catalyzed a,/ -elimination with a mechanism similar to serine dehydrase and cysteine desulfhydrase (45). The coenzyme is probably bound as a Schiff base with an amino group of the enzyme since there is an absorption maximum at 415 nm in solutions of the purified garlic enzyme (40). The inhibition by L-cysteine is presumably caused by formation of a thiazolidine with the coenzyme (46). Added pyridoxal-5-phosphate also combines directly with the substrate. The dissociation constant for the complex is about 5 X lO M. When this is taken into account, the dissociation constant of the holoenzyme can be shown to be about 5 X 10 M (47). The higher enzyme activity in pyrophosphate buflFer than in Tris or phosphate may be explained by pyrophosphate chelation of metal ions which otherwise form tighter complexes with the substrate and coenzyme (47). This decreases the availability of added coenzyme. 

Wang, C. L., Lum, A. M., Ozuna, S. C., Clark, D. S., and Keasling, J. D. (2001). Aerobic sulfide production and cadmium precipitation by Escherichia coli expressing the Treponema denticola cysteine desulfhydrase gene. Appl. Microbiol. Biotechnol. 56, 425-430. 

Kredich, N.M., L.J. Foote, and B.S. Keenan. 1973. The stoichiometry and kinetics of the inducible cysteine desulfhydrase from Salmonella typhimurium.. Biol. Chem. 248 6187-6196. 

Degradation of L-cysteine by cysteine desulfhydrase or other PLP enzymes present in the cells was successfully prevented by addition of hydroxylamine or semi-carbazide to the incubation mixture. A mutant strain of Ps. thiazolinophilum lacking cysteine desulfhydrase was isolated and used to produce L-cysteine from d,l-ATC in a molar yield of 95% and at a product concentration of 31.4 g L 1[12S. Pseudomonas desmolytica A] 3872, one of the L-cysteine producers isolated was found to lack the ability to convert d-ATC into L-cysteine it is an ATC racemase-deficient strain 129l. However, little is known about the enzymological properties and function of the racemase. 

In all reactions, the first stage is formation of SchifTs base a by condensation of PalP and the amino acid. Schiff s bases a and b represent part of transamination, but for the complete mechanism see Transamination. Racemization a- b, followed by b-ia-iamino acid-1-PalP, with addition of the proton in the opposite configuration. Amino acid decarboxylation a -> d- c - amine + PalP. Serine hydroxymethyltransferase (EC 2.1.2.1) X = OH L-serine + PalP a f- g glycine + PalP reversal of these reactions leads to L-serine synthesis from glycine the hydroxymethyl group is carried by te-trahydrofolic acid. Cysteine desulfhydrase (EC 4.4.1.1) X = SH cy eine + PalP a b-> c-y hydro-... 

Corroborative evidence has been obtained from experiments with isolated tissue preparations. The in vitro formation of cystine by liver slices (and a saline extract) was observed in nuxtures containing dl-homocysteine and DL-serine. Neither substance was effective when incubated alone. The L-forms of the two amino acids were implicated in the reaction, as D-homocysteine and o-serine did not substitute for the DL-forms and the isolated cystine had the L-configuration. The reaction proceeded best under anaerobic conditions and in the present of O.OOlAf CN , as the latter inhibits cysteine desulfhydrase activity. Methionine substituted very poorly for homocysteine in vitro. 

Hassan, S.S.M.,E1-Baz, A.E., Abd-Rabboh, H.S.M., 2007. A novel potentiometric biosensor for selective L-cysteine determination using L-cysteiine-desulfhydrase producing Tridiosporonjirovecii yeast cells coupled with sulfide electrode. Anal. Chim. Acta 602, 108—113. 

---