Multichain mechanism

The enzyme is always bound to the polymer chain in this one-chain mechanism. Multichain mechanisms are much more common. In these, the enzyme disengages after every linking step and thus wanders from chain to chain (see also polycondensation. Chapter 17). In the multichain mechanism, the enzyme and the substrate form an enzyme-substrate complex ES in the first step ... 

The following mechanism emerges form the observation reported so far on the colloidal stability of multichain PNIPAM particles at elevated temperature. Let us note first that such PNIPAM particles are examples of mesoglob-ules, according to the definition of Timoshenko and Kuznetsov [215] ... 

Whelan and Bailey were also able to clarify the polymerization mechanism of the enzymatic polymerization with phosphorylase [124], Their results showed that the polymerization follows a multichain scheme in contrast to a single-chain scheme that was also proposed by some authors. In the multichain polymerization scheme, the enzyme-substrate complex dissociates after every addition step, whereas in the single-chain scheme each enzyme continuously increases the length of a single primer chain without dissociation. 

Dynamic Monte Carlo simulations were first used by Verdier and Stockmayer (5) for lattice polymers. An alternative dynamical Monte Carlo method has been developed by Ceperley, Kalos and Lebowitz (6) and applied to the study of single, three dimensional polymers. In addition to the dynamic Monte Carlo studies, molecular dynamics methods have been used. Ryckaert and Bellemans (7) and Weber (8) have studied liquid n-butane. Solvent effects have been probed by Bishop, Kalos and Frisch (9), Rapaport (10), and Rebertus, Berne and Chandler (11). Multichain systems have been simulated by Curro (12), De Vos and Bellemans (13), Wall et al (14), Okamoto (15), Kranbu ehl and Schardt (16), and Mandel (17). Curro s study was the only one without a lattice but no dynamic properties were calculated because the standard Metropolis method was employed. De Vos and Belleman, Okamoto, and Kranbuehl and Schardt studies included dynamics by using the technique of Verdier and Stockmayer. Wall et al and Mandel introduced a novel mechanism for speeding relaxation to equilibrium but no dynamical properties were studied. These investigations indicated that the chain contracted and the chain dynamic processes slowed down in the presence of other polymers. 

Coombes and Katchalski [29] have considered a slightly more complex version of this mechanism in which a second propagation coefficient operates above a critical degree of polymerization. Katchalski et al. [30] calculated the molecular weight distribution obtained in a system following scheme (12) but also including a bimolecular termination step. Various authors have analysed more complex systems in which the initiator is a polymeric species. Thus Gold [31] has shown that initiation by a poly a-amino acid with a Poisson distribution leads to a polymeric product with an over-all Poisson distribution, and Katchalski et al. [32] demonstrated that in multichain polymers synthesized from polyfunctional initiators Poisson distributions also arise. 

A third mechanism, proposed by French,involves multiple attack, in which the enzyme remains associated with a given substrate molecule long enough to remove several maltose residues before attacking another amylose molecule. With amylose of DP 44, sweet-potato /3-amylase removed about four maltose residues per effective encounter. i The multiple-attack mechanism is, in fact, intermediate between the single-chain and multi-chain patterns. In agreement with this view, Whelan and Bailey found that the action of /3-amylase on maltosaccharides of DP 6 and 7 and on amylose of DP 49 was intermediate between single-chain and multichain, but varied with the pH and temperature of the experiments. 

Although the synthesis of amylose by P-enzyme proceeds by a multichain mechanism, the reverse reaction shows some degree of single-chain action. The final products of phosphorolysis are a-D-glucosyl phosphate and maltopentaose. 

Tacryl . Acrylic fiber of a specific multi chain type. The structure conld he described as a Spider molecule with up to siit long straight linear legs which can orient independently and build up a fibrous structure. The molecular structure is built up by a controlled cross-linking process, so that Tacryl is like wool as it has a specific chain molecular interlinking which contributes to its mechanical and elastic properties. Synthesis of multichain polymers Schaefgen,... 

Synthesis of the skeletal chains must proceed, as do all enzyme-controlled polymerization reactions, either by a single or a multichain reaction mechanism, through a series of "growing cycles in which the... 

A third definition considers what happens at the actual site of reaction. A chain is joined to a monomer or another chain in each polyreaction. The monomer or other chain may add on to or insert in to the chain being considered. The initiator may be a chain starter or a catalyst and so, may be associated always with one individual chain (one-chain mechanism) or change from chain to chain (multichain mechanism). One can distinguish between... 

The preceding derivations relate to a multichain mechanism with one catalytically active group per enzyme molecule. If the enzyme molecule has N equally and quite independently active groups, then Equation (19-54) is modified to... 

The DC has been associated with the presence of multichain domains (clusters) with dimensions appreciably exceeding the size of single chains. Both, the origin of these domains as well as the mechanism by which macromolecules of the same charge interact themselves are not satisfactorily understood. The DCs has been found in a wide variety of synthetic and biological polymers. Therefore, it appears that it is a universal property of charged macromolecules dispersed in polar solvents [7]. 

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