Lyase reactions

Fig. 2.— Activity47 of Tomato Pectinesterase (PE) in the Presence (1) and Absence (2) of Exopectate Lyase. [Reaction mixtures contained 0.125% of poly(D-galacturonic acid methyl ester) methyl glycoside, 0.5 mM CaCl2, 2.8 units of pectinesterase, and, in the reaction mixture represented by curve 1, 1.5 unit of lyase.] Reprinted, with permission, from M. Lee and J. D. Macmillan, Biochemistry, 9, 1930-1934 (1970). Copyright by the American Chemical Society.

A specialized amino acid residue that serves as an essesn-tial electrophilic center in several enzymatic reactions, including those catalyzed by L-phenylalanine ammonia lyase (Reaction L-phenylalanine tranx-cinnamate + NH3) and L-histidine ammonia lyase (Reaction L-histi-dine urocanate + NH3). The former facilitates the elimination of ammonia and the pro-S hydrogen of phe-nylanine, and the initial step is nucleophilic attack of... 

Evidence was also provided that Insoluble residues may be produced from GSH conjugates via cysteine conjugate or thiol Intermediates. These studies also suggested that certain reactions should be studied in greater detail to assess their importance in pesticide metabolism l.e., the C-S lyase reaction, the methyl transferase reaction, and the transamination reaction. 

D. In addition to its abihty to block steroid biosynthesis, ketoconazole is frequently used as an antifungal agent. Its action is readily reversible and is used principally for interim management of Cushing s disease prior to surgery or radiotherapy. Ketoconazole preferentially blocks the C17,20 lyase reaction that is involved in the synthesis of sex steroids. 

Pyruvate formate-lyase reaction. Anaerobic cleavage of pyruvate to acetyl-CoA and formate (Eq. 15-37) is essential to the energy economy of many cells, including those of E. coli. No external oxidant is needed, and the reaction does not require lipoic acid. 

The details of the process and the oxidation-reduction balance can be pictured as in Eq. 17-25. Pyruvate is cleaved by the pyruvate formate-lyase reaction (Eq. 15-37) to acetyl-CoA and formic acid. Half of the acetyl-CoA is cleaved to acetate via acetyl-P with generation of ATP, while the other half is reduced in two steps to ethanol using the two molecules of NADH produced in the initial oxidation of triose phosphate (Eq. 17-25). The overall energy yield is three molecules of ATP per glucose. The "efficiency" is thus (3 x 34.5)... 

Use the pyruvate formate-lyase reaction. What yield of ATP do you expect per molecule of glucose fermented ... 

An individual has been found who is missing malic enzyme in his cytoplasm. He has instead an enzyme that converts the oxalacetate made from the citrate lyase reaction directly to pyruvate and C02. Discuss this patient in terms of the likely effect of these changes on his ability to synthesize fatty acids. 

It has since been proved that malate synthase proceeds with inversion independently of any assumption about isotope effect. This has been done via a lyase system that splits malate to acetate21—a methylene-to-methyl conversion. By using methylene-labeled malate and generating chiral acetate, it could be shown unambiguously that this cleavage is an inversion. When the lyase reaction was applied to malate formed from chiral acetate by malate synthase, it was found that the acetate thus generated was of the same chirality as the starting material. This proved that there is also inversion in the reaction of malate synthase. 

With the stereochemistry of the citrate lyase reaction determined, that of the Si citrate synthetase (the common enzyme) was established as shown in Fig. 70. Condensation of (J )-acetic-d, t acid (configuration known by synthesis) with oxalo-acetate gives what turns out to be mainly (2S,3/ )-citric-2-d,2-/ acid (112).41 When this acid is then cleaved with citrate lyase, the major product is (/ )-acetic-d, t acid, as established by the malate synthetase/fumarase diagnosis. It follows that both the Si-citrate synthetase and citrate lyase reactions must involve the same stereochemical course. Since that of the lyase reaction is inversion (vide supra), that of the Si synthetase reaction must be inversion also. And since the overall stereochemical result shown in Fig. 70 is not dependent on the magnitude of the... 

Because the H/D isotope effect is not infinite, there will also be some (2/J,3/f)-citric-2-r acid in which the deuterium was abstracted from the acetyl-CoA. This material will give CH2TC02H in the citrate lyase reaction which, being achiral, behaves like racemic CHDTC02H in the subsequent steps. 

A second type of reaction whose stereochemistry was elucidated by the use of chiral methyl groups is of the CDTXY->CHDTX type, exemplified by the citrate lyase reaction (Fig. 69). The stereochemical outcome of a number of these reactions has also been tabulated 149). 

R. W. Guynn and R. L. Veech, The equilibrium constants of the adenosine triphosphate hydrolysis and the adenosine triphosphate-citrate lyase reactions, J. Biol. Chem. 248, 6966 6972 (1973). 

A Skolaut, J Retey (2001) 1,4-Dihydrophenylalanine - its synthesis and behavior in the phenylalanine ammonia-lyase reaction Archiv Biochem Biophys 393(2) 187-191... 

Fig. 31. A metastable trigonal intermediate in the lyase reaction results in the loss of stereospecificity.

Chapter 11 Lyase Reactions (Class 4), Isomerase Reactions (Class 5), and Ligase Reactions (Class 6) at 298.15 K... 

Standard Transformed Gibbs Energies of Reaction, Changes in Binding of Hydrogen Ions, and Apparent Equilibrium Constants of Lyase Reactions... 

A table is prepared to show the range of apparent equilibrium constants for lyase reactions at 298.15 K, pH 7, and 0.25 M ionic strength. 

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