Lyase, enzymatic activity

There is a fifth bifunctional enzyme which catalyzes reactions 8 and 12 of the purine pathway (Fig. 15-16) but adenylosuccinate lyase has one active site with dual specificity, catalyzing both reactions (SA1CAR—> AICAR, sAMP—> AMP Fig. 15-16). All 14 enzymatic activities of Fig. 15-16 are cytosolic and there is a variety of evidence for association of subsets of these activities in vivo. The existence of a pathway particle or metabolon" for de novo purine biosynthesis in intact cells has been proposed. 

The widely accepted basis of all enzyme classifications are the recommendations of the Enzyme Committee (E.C.) of the International Union of Biochemistry and Molecular Biology (IUBMB)1491. Within this system, enzymatic activities are classified by a four-level hierarchy and each entry is described by a set of four numbers. The first number describes the top level and can be either 1 for oxidoreductases, 2 for transferases, 3 for hydrolases, 4 for lyases, 5 for isomerases or 6 for ligases. The meaning of the three lower hierarchy levels depends on the top level group. As an example, glycogen synthase is classified as 2.4.1.11 here, the 2 stands for transferases, the 4 for glycosyl-transferases, the 1 for hexosyl-transferases and the 11 for the particular subfamily. 

Microsomal cytochrome P-450 from neonatal pig testis Two enzymatic activities (17ce-hydroxylase and C17,20-lyase) associated with one protein. Biochemistry 20, 4037-4042. 

Promising results using hydroxynitrile lyases were achieved by Gaisberger et al. and Lou et al. in tetrafluoroborate-based ionic liquids, especially when using the enzyme from Prunus amygdalus. Gaisberger et al. used the lyases for reactions with long chain aldehydes. Lou et al. discovered increased thermal enzyme stability, improved enantioselectivity and enzymatic activity for a transcyanation reaction at low ionic liquid contents in buffer solution [52,53]... 

All tailed phages have evolved tailspike and fiber proteins for efficient virus-host-interactions. These specialized adhesions mediate the recognition and attachment to the bacterial surface and constitute the key determinants for host specificity. Interestingly, many spikes and fibers are composed of homotrimeric complexes which remain stable even in the presence of sodium dodecyl sulfate (SDS) [12, 14, 30-34], Several phages have developed tailspike proteins with an enzymatic activity in order to penetrate the thick layer of lipopolysaccharides or capsular polysaccharides of many pathogenic bacteria. These capsule-specific depolymerases (hydrolases or lyases) are required to gain access to and to fix the phage at the bacterial outer membrane [13, 14, 35-38]. 

Enzymatically active materials (fruits, vegetables and some fats) contain a large number of other aldehydes that are produced from essential fatty acids, mainly linoleic and Knolenic acids (Table 8.9) by oxidation reactions catalysed by lipoxygenases. In some vegetables (e.g. in cucumbers), aldehydes also result from a-oxidation of fatty acids (Figure 8.15). The primary oxidation products of essential fatty acids are hydroperoxides, which break down to aldehydes and other products under the action of lyases and can be... 

The addition of pectolytic enzymes in crushed grapes can improve juice extraction for certain varieties very rich in pectic substances (Muscat, Sylvaner, etc.). Commercial preparations contain diverse enzymatic activities which are active at a low pH pectin methyl esterases, polygalacturonases, pectin lyases and hemicellulases. At a concentration of 2-4 g/hl, 15% more juice can be obtained during a settling period of 4-10 hours even a shorter settling period (1-2 hours) increases the proportion of free run (Table 11.8). Effectiveness varies according to the nature of the grapes. 

J.P. Montgomery, J.J. Schmber, P.J. Vollmer, H-H Yang, Method for stabilizing the enzymatic activity of phenylalanine ammonia lyase during hphenylalanine production. Cenex Corporation, US 4,584,269 A, 1985. 

Hernandez, L., Luna, H., Rulz-Teran, F. and Vazquez, A. (2004) Screening for hydroxynitrile lyase activity in crude preparations of some edible plants. Journal of Molecular Catalysis B-Enzymatic, 30, 105-108. 

Costes, D., Wehtje, E. and Adlercreutz, P. (2001) Cross-linked crystals of hydroxynitrile lyase as catalyst for the synthesis of optically active cyanohydrins. Journal of Molecular Catalysis B-Enzymatic, 11, 607-612. 

In the first enzymatic step, phenylalanine ammonia lyase (PAL) converts phenylalanine to trans cinnamate, via a deamination reaction liberating ammonia. PAL can also convert tyrosine to p-coumarate, albeit at lower efficiency (MacDonald and D Cunha 2007). PAL functions as a tetramer of identical subunits, with two subunits combining to form one active site (Stafford 1990 MacDonald and D Cunha 2007). 

Enzymatic preparations for PAL from monocotyledonous species (monocots) can show a similar activity against tyrosine (tyrosine ammonia lyase, TAL), and TAL enzymatic preparations also show PAL activity. That a single enzyme may account for the observed cooccurring TAL and PAL activities was confirmed by Rosier et al., who showed the recombinant Zea mays (maize) PAL converted tyrosine to 4-coumarate directly, thus removing the requirement for the usual 4-hydroxylation step in phenylpropanoid biosynthesis. 

Although many biochemical reactions take place in the bulk aqueous phase, there are several, catalyzed by hydroxynitrile lyases, where only the enzyme molecules close to the interface are involved in the reaction, unlike those enzyme molecules that remain idly suspended in the bulk aqueous phase [6, 50, 51]. This mechanism has no relation to the interfacial activation mechanism typical of lipases and phospholipases. Promoting biocatalysis in the interface may prove fruitful, particularly if substrates are dissolved in both aqueous phases, provided that interfacial stress is minimized. This approach was put into practice recently for the enzymatic epoxidation of styrene [52]. By binding the enzyme to the interface through conjugation of chloroperoxidase with polystyrene, a platform that protected the enzyme from interfacial stress and minimized product hydrolysis was obtained. It also allowed a significant increase in productivity, as compared to the use of free enzyme, and simultaneously allowed continuous feeding, which further enhanced productivity. 

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