Lyase enzymes

The first step in the biological degradation of histidine is formation of a 4-methylideneimidazol-5-one (MIO) by cyclization of a segment of the peptide chain in the histidine ammonia lyase enzyme. Propose a mechanism. 

Mushrooms have been investigated with especial reference to shiitake, Lentinus edodes, the flavorful fungus widely used in Chinese and Japanese dishes. While the umami taste is attributed to guanylic acid, lentinic acid 14 (Scheme 6) is converted to lenthionine, 1,2,3,5,6-pentathiacycloheptane 15, a compound with the characteristic shiitake flavor. This complex reaction requires a C-S lyase enzyme.30 Other important flavor compounds are 1,2,4,6-tetrathiacycloheptane 16 (Scheme 6) and 1,2,3,4,5,6-hexathiacycloheptane (not shown). 

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... 

In simple terms, the global sulfur cycle has two components. One is biochemical involving the conversion of sulfate to sulfide and the formation of DMS the other is atmospheric photochemical oxidation of DMS to sulfur oxyacids. DMS is formed mainly in the oceans by microorganisms and to a lesser extent in plants. About 38M0 Tg year-1 of DMS are released to the atmosphere from the oceans. The major precursor for DMS formation is the sulfonium salt, dimethylsulfoniopropionate, (CH3)2 S+ CH2 CH2 COOH, DMSP. DMSP lyase enzymes catalyze an elimination of acrylic acid from DMSP (Equation 12) with the release of DMS ... 

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. 

Lyases. Enzymes that catalyse the cleaving of bonds by reactions other than hydrolysis. 

The immediate precursor of pentachlorothiophenol was assumed to be S-(PCP)Cys. Cysteine C-S lyase enzymes that convert S-aryl and S-alkyl derivatives of cysteine to pyruvate and a thioalcohol have been detected in some plant species (24,. When the... 

Pentachlorothiophenol was formed Iji vitro from S-(PCP)Cys by a C-S lyase enzyme from onion root. This enzyme was active with S-(PCP)Cys, S-(2,M-dinitrophenyl)cysteine, and the cysteine conjugate of propachlor. A C-S lyase from Alblzzla lophanta was previously shown to utilize a broad range of cysteine derivatives (2U). 

If the (3-lyase enzyme, or the renal basolateral membrane transport system, or y-glutamyltransferase, or cysteinylglycinase is inhibited, the nephrotoxicity of DCVC can be reduced, indicating that each of these processes is involved. 

Lyases. Enzymes promoting addition to double bonds or the reverse. 

Tanaka, H., Esaki, N., and Soda, K. (1985). A versatile bacterial enzyme L-methionine y-lyase. Enzyme Microbiol. Technol. 7,530-537. 

R.R. Walters, P.A. Johnson and R.P. Buck, Histidine ammonia-lyase enzyme electrode for determination of L-histidine, Anal. Chem., 52 (1980) 1684-1690. 

Aliphatic aldehydes have been converted to their (R)-cyanohydrins using a bipha-sic system to accommodate hydroxynitrile lyase enzyme (from the Japanese apricot, Prunus mume) as the enantioselective catalyst.251... 

Algae can adjust the intracellular concentration of DMSP through the biosynthetic (anabolic) or the degradation (catabolic) pathways. DMSP-lyase enzymes facilitate the degradation pathway, in which DMSP is cleaved to DMS, acrylate and a proton. What controls the activity of DMSP-lyases in phytoplankton is still unknown. Stefels (2000) suggested... 

Adenyl cyclase, also referred to as adenylate cyclase or adenylyl cyclase, is a lyase enzyme (in biochemistry, a lyase is an enzyme that catalyses the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure. Lyases differ from other enzymes in that they only require one substrate for the reaction in one direction, but two substrates for the reverse reaction). There are 10 known adenyl cyclases in mammals, ADCYl through ADCYIO. 

It is possible that racemization of some of the amiiio aeids, such as cystine, serine, and threonine, occurs during extraction and accounts for some of the complexity of wool protein fractions (Lindley, unpublished observations, 1962). Performic acid, however, used in the preparation of the keratoses did not produce racemization in proteins (Hill and Smith, 1957). It has not proved possible to solve uneciuivocally the problem of whether or not the reduction and alkylation pi oceduros used in the preparation of SCM kerateiues cause racemization. Lindley (unpublished, 1961) has shown that S -carboxymethyl cysteine isolated from acid hydrolyzates of SCM kerateines is partially racemized as measured both by direct optical rotation procedures and also by the use of a C-S lyase enzyme which is specihe for the n-form (Schwinuner and Kjaer, 1960). Control experiments showed, however, that L-S-carboxymethyl cysteine itself is partially racemized on refluxing with 5 N acid, and when allowance was made for this it appeared that the amount of racemization attributable to the reduction and alkylation procedures was small (less than 5 %) even when the most drastic conditions (pH 12.5 and 50°C) were used to prepare the SCM kerateines. Since S-carboxymethyl cysteine in peptide combination may well racemize more readily on acid hydrolysis than does the free amino acid, even this may be an over-estimate, and it would seem unlikely therefore that racemization is a serious problem in SCM kerateines as presently prepared. 

Hatanaka shows in detail the reaction scheme in plants whereby linolenic acid is converted via lipoxygenase and lyase enzymes to cis-3-hexenal. This is subsequently converted by other enzyme systems to leaf aldehyde and leaf alcohol. These three aroma chemicals are important "green" aroma notes in strawberries and other berries. If these enzymes were commercially available, then the production of natural cis-3-hexenal from inexpensive vegetable oil is theoretically feasible. 

The mechanism by which xenobiotic alcohols or esters are converted to fatty acid esters has not been studied. They could be formed by the action of lyase enzymes in the presence of fatty acid glyceryl esters, as in the conversion of farnesol to farnesol fatty acid esters (150). Some lipolytic acyl hydrolase enzymes from plants readily catalyze the transfer of lipid-bound fatty acids to low MW alcohol acceptors (150.151) and enzymes of this class could be responsible for the occasional formation of fatty acid conjugates of xenobiotic alcohols. Mechanisms involving fatty acid acyl CoA, phospholipids, or direct esterification with fatty acids might also be involved (1 ). 

Historically, L-aspartic acid was produced by hydrolysis of asparagine, isolated from protein hydrolysates, or by the resolution of chemically synthesized d,l-aspartate. With the discovery of aspartase (L-aspartatc ammonia lyase. Enzyme Commission [EC] 4.3.1.1) [5] fermentation routes to L-aspartic acid quickly superseded the initial chemical methods. After further characterization, enzymatic routes to the production aspartic acid from ammonium fumarate using aspartase 317... 

The reason why these enzymes have received considerable attention over the years is that they display a high degree of enantiotopic selectivity on the prochiral aldehyde and ketone substrates. The selectivity of these enzymes is in many instances masked by the rate of spontaneous racemization of the cyanohydrins, which are prone to racemization under non-acidic conditions. This balance of selectivity of the enzymes versus the competition with the spontaneous racemization reaction as a function of the pH was described as early as 1921 using the hydroxynitrile lyase enzyme from peach leaves [22], These early experiments describe one of the challenges of applying hydroxynitrile lyases on an industrial scale. 

Lyases enzymes cleaving, typically, C-C, C-O or C-N bonds by elimination, typically leaving double bonds. 

Other C-0 lyase enzymes include aconitate hydratase or aconitase (E. C. 4.2.1.3), an enzyme that catalyzes two tricarboxylic acid cycle steps from isocitric acid to citrate (14)1141 or vice versa, via the intermediate cis-aconitate (13). Citrate dehydratase (E. C. 4.2.1.4) is only capable of converting citrate to cis-aconitate and does not act on isocitrate (15) 115l... 

Bandhuvula, P., Fyrst, H., and Saba, J.D., A rapid fluorescent assay for sphingosine-1-phosphate lyase enzyme activity, J Lipid Res, 48 (2007) 2769-2778. 

In some favorable cases, such as with BAL, the CD band for the predecarboxylation intermediate (via the IP form) could be observed from the slow substrates benzoylformate or phenylpyruvic acid. This is feasible since BAL, while a carboligase/lyase enzyme, also catalyzes decarboxylation of aromatic 2-oxoacids, albeit very slowly. 

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