Enzymes cooperative action

Desaturation requires the cooperative action of two enzymes Cytochrome b5 reductase and stearoyl-CoA desaturase, in addition to an electron carrier protein, cyto-... 

Figure 1. Cooperative action of enzymes of the cellulase system in hydrolytically converting cellulose to glucose...

Generally speaking, the role of the enzyme consists of the selective and specific attraction of substrate and the highly efficient catalysis. Every enzyme has its own characteristic feature for example, the specificity in the binding and a charge-relay action in the catalysis in a-chymotrypsin, the contribution of the imidazole moiety as an electron donor to the electrophilicity of zinc ion in carboxypeptidase, the change in the spin state and the reactivity of the transition metal ion by the coordination of the imidazole in the hemochrome. These typical characteristic features are the result of the cooperative actions of the constituents. 

This article describes the cooperative action in which the nucleophile-containing polymer is studied as the model of the enzyme. 

One possible way to solve this problem is to combine another enzyme, like SP, which produces a-GlP for GP. Waldmann and colleagues reported the combined use of SP and GP for the production of amylose from sucrose (1986). In this system, SP catalyzes the phosphorolysis of sucrose to produce a-GlP and fructose, and the a-GlP is next used as a substrate of GP to produce amylose. An interesting feature of this SP-GP system is that Pi produced in the second GP reaction is used as a substrate for the first SP reaction. The cooperative action by the two phosphorylases proceeds continuously with a constant Pi concentration, without any inhibition caused by an accumulation of Pi. Based on this SP-GP system, we have now established the process to manufacture essentially linear amylose with controlled molecular size, by using thermostable variants of SP and GP (Yanase et al., 2007 Ohdan et al., 2007). 

In nature a cascade of enzyme-catalyzed reactions is involved for the biosynthesis of starch. When selecting the appropriate enzymes and reaction circumstances reactions with multiple enzymes can be performed in vitro. Synthetic glycogen was first synthesized in vitro by Cori [146] in 1943 via the cooperative action of muscle phosphorylase and branching enzymes isolated from rat liver and rabbit heart. 

Cooperative action, often designated synergy, of the three cellulolytic enzyme classes is essential for an efficient enzymatic hydrolysis process [181]. 

Incorporation of the cysteinyl residue 6 ould be partkularly interestir because of its pivotal role in the sulfhydry enzymes and the high nucleo iilicity of the SH group. A 1 1 copdiymer of L-cystein 6 and L-glutamic acid 2 ows catalytic activity toward PNPA (139). The pH-rate profQe is composed of two maxima as shown in Fig. 7—1. These maxima do not coincide with maxima found for homopolymers of glutamic acid and of cystein, and the cooperative action of the two functional groups was implied for tiie copolymer. A 1 1 copolymer of L-cystein 6 and L-aspartic acid 3 was inactive. 

Cooperative action of the functional groups of the enzyme is important for this enzymatic catalysis as for many other enzymatic reactions. 

Evidence for the direct electron transfer from PPy to an entrapped quinohemoprotein alcohol dehydrogenase (QH-ADH) from Gluconobacter sp.33 prepared via an in situ polymerization of pyrrole in the presence of QH-ADH has been demonstrated by Ramanavicius et aL [70]. It was proposed that the cooperative action of the pyrroloquino-line-quinone (PQQ) and heme-containing enzymes permit electron transfer from the enzyme active site to the ICP. Ethanol is said to diffuse to the PQQ enzyme centre where it is oxidized to an aldehyde. The PQQ centre is subsequently regenerated by the heme sites in the enzyme. Resulting is an electron that can be readily transferred to the PPy at a viable kinetic rate. 

Fig.l. Fatty acid biosynthesis, Cooperative action of the proteinsof fatty acid synthase, which may be a multienzyme compiex, or a single multifunctional protein (see Table2). The zig-zags represent the movable pantetheine arm of the acyl carrier protein. The central circle represents acyl carrier protein the other enzymes are represented by the six peripheral circles (see Table 1). This purely diagrammatic representation does not necessarily show the true juxtaposition of the proteins. 

Cooperative mechanism disuifide reductase (disuifide bond reducing) and peptidases (cieaving peptide bonds in keratin). This mechanism was described by Yamamura et ai. (2002) in Stenotrophomonas sp. None of these enzymes showed keratinoiytic activity independentiy and the cooperative action of the two enzymes resuits in the effective degradation of keratin. Extraceiiuiar peptidases acted on the dissociated poiymers, hydroiyzing them into peptides/amino acids... 

Figure 18.9 shows the pH-activity profiles of the native and complexed enzymes using BANA as the low molecular weight substrate. The complexed BT is found to have an appreciable retention of enzymatic activity. This finding indicates that one imidazolyl group (histidine), which cooperates with both COOH (aspartic acid) and OH (serine) in acylation-deacylation as an intermediate step in the enzyme catalytic action [22], is free of salt linkages with KPVS. 

Figure 10. Cooperative action of a3-NeuAcT (a3-ST, dashed arrow), a3-FucT IV (myeloid enzyme a3-FT, thin solid arrow), and a3-FucT VII (a3-FT, leukocyte enzyme bold solid arrow) in the synthesis of sialyl-oligomeric Lewis and related structures on polylactosaminoglycan chains. F, Fuc G, Gal GN, GlcNAc LAG, polylactosaminoglycan SA, NeuAc.

The metabolic breakdown of triacylglycerols begins with their hydrolysis to yield glycerol plus fatty acids. The reaction is catalyzed by a lipase, whose mechanism of action is shown in Figure 29.2. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine residues, which act cooperatively to provide the necessary acid and base catalysis for the individual steps. Hydrolysis is accomplished by two sequential nucleophilic acyl substitution reactions, one that covalently binds an acyl group to the side chain -OH of a serine residue on the enzyme and a second that frees the fatty acid from the enzyme. 

Figure 29.2 MECHANISM Mechanism of action of lipase. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine, which react cooperatively to carry out two nucleophilic acyl substitution reactions. Individual steps are explained in the text.

The relationship between substrate concentration ([S]) and reaction velocity (v, equivalent to the degree of binding of substrate to the active site) is, in the absence of cooperativity, usually hyperbolic in nature, with binding behavior complying with the law of mass action. However, the equation describing the hyperbolic relationship between v and [S] can be simple or complex, depending on the enzyme, the identity of the substrate, and the reaction conditions. Quantitative analyses of these v versus [S] relationships are referred to as enzyme kinetics. 

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