Depolymerization polymeric substrates

Although some depolymerases act processively in cleaving their polymeric substrates, others act by what can be described as multiple attack which results in nonselective scission or random scission. The analysis of cleavage products during the course of enzyme-catalyzed depolymerization can provide important clues about the nature of the reaction. With random scission, the rate of bond scission must be proportional to the total number of unbroken bonds present in the solution. Thomas measured the rate of base addition in a pH-Stat (a device with an automated feedback servomotor that expels ti-trant from a syringe to maintain pH) to follow the kinetics of DNA bond scission by DNase. The number of bonds cleaved was linear with time, and this was indicative of random scission. In other cases, one may apply the template challenge method to assess the processivity of nucleic acid polymerases. See Processivity... 

The use of rf cold plasmas to cause polymerization of monomers on such non-conducting substrates as glasses (6) and other polymeric substances (7) is not new. However, the chemistry involved in rf cold plasmas is complicated, and within the reactor, depolymerizations of substrates and of newly formed polymers occur simultaneously with polymerization reactions. Clark (8) has reported on such phenomena, and it is known that the relative rates of polymerization to depolymerization vary within the reactor. 

Intrigued by the finding that Eca PLs exhibit notable differences in their kinetics, HPAEC analyses were carried out to examine the products from the depolymerization of PGA and 31% esterified pectin. After 18 h of incubation with PGA, PL1 and PL2 had produced mainly di- and trimers. Similariy, main products of PL3 action were trimers, followed by dimers. Moreover, it was the only enzyme found to produce monomers from unesterified substrates with a degree of polymerization >3. Using 31% esterified pectin as a substrate, similar end products were released by the PLs as from PGA. In addition to the products described, traces of tetra- up to octamers were detectable. While PL1 and PL2 released di- and trimers at almost... 

A quite different mechanism for altering subunit interactions is through polymerization-depolymerization of subunits.54,55 If different polymeric states of the enzyme have different turnover numbers and/or different affinities for substrates and effectors, a model can be generated that is similar to the MWC model except that the cooperativity is also dependent on the enzyme concentration. Both K and V systems are possible with all the models. 

The amorphous phase appearing above 20 GPa at room temperature (see above) has also recently been studied by X-ray diffraction [135] and Raman scattering [132,133]. Serebryanaya et al. [135] identify the structure as a three-dimensionally polymerized Immm orthorhombic lattice, but find that compression above 40 GPa gives a truly amorphous structure. In contrast to the orthorhombic three-dimensional polymer structure discussed in the last section, the best fit here is found for (2+2) cycloaddition in two directions, with (3+3) cycloaddition in the third, and thus some relationship to the tetragonal phase. From the in situ X-ray data a bulk modulus of 530 GPa is deduced, about 20% higher than for diamond. Talyzin et al. [132, 133] find that this phase depolymerizes on decompression into linear polymer chains, unless the sample is heated to above 575 K under pressure. A strong interaction with the diamond substrate is also noted, such that only films with a thickness of several hundred nm are able to polymerize fully [ 132]. Hardness tests were also carried out on the polymerized films, which were found to be almost as hard as diamond and to show an extreme superelastic response with a 90% elastic recovery after indentation [133]. 

This is a report of a study to use depolymerization or degradation and polymerization reactions within the rf reactor to advantage in the formation of new polymers and to Investigate the relative contributions of rf produced particles (electrons and ions) and of rf produced uv light in the Initiation of graft polymerizations on cotton substrates. 

In this chapter, we have focused on the mechanics of a single cell and an assembly of polarized cells adhered to an elastic substrate. We started with the description of force generators and tension bearing elements within the cell cytoskeleton. We have discussed how dynamics of cytoskeletal filaments are affected by the concentration of monomeric subunits. During polymerization and depolymerization process, these polymers are able to generate stresses that are essential for cell functioning, but not limited to, cell adhesion, shape modulation, migration and tissue formation. 

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