Stability of the filament

Most eukaryotic cells contain the major cytoskeletal protein, actin, which can exist as a monomer (G-actin) and reversibly polymerize into long filamentous structures (F-actin). The F-actin filament is polarized such that the rates of polymerization and depolymerization are different at the two ends. At the plus end (also called barbed end) monomer addition occurs readily, relative to the minus end (also called pointed end) where polymerization is less favored. In addition, the actin subunit binds adenine nucleotides and has an intrinsic ATPase activity. ATP-actin binds preferably at the plus end and, after incorporation into the filament, is converted to ADP-actin. These properties have a significant impact on the dynamics and stability of the filament [54, 293]. In the cell, polymerization and depolymerization are highly regulated reactions, this regulation being mediated by multiple actin-binding proteins. 

In the spinning process, the molecular chains are oriented by three effects flow orientation inside and outside the spinneret orifices, and orientation by deformation. For the orientation of the molecular chains that occurs in the spinneret to be effective in orienting the filament, the rate of stabilization of the filament must be greater than the reciprocal relaxation time. This requirement applies only to the surfaces and not to the interior of the filament. The orientation of the molecule within the spinneret thus has little influence on the orientation of the molecule in the finished filament. 

Phalloidin binds to polymeric, or filamentous, actin and thereby enhances the stability of the filaments to such an extent that the rate of depolymerization is close to zero. All toxic effects caused by phalloidin are understood as consequence of this stabilization effect. 

Polymer growth J(c) showed nonlinear monomer concentration dependence in the presence of ATP (Carrier et al., 1984), while in the presence of ADP, the plot of J(c) versus monomer concentration for actin was a straight line, as expected for reversible polymerization. The data imply that newly incorporated subunits dissociate from the filament at a slower rate than internal ADP-subunits in other words, (a) the effect of nucleotide hydrolysis is to decrease the stability of the polymer by increasing k and (b) nucleotide hydrolysis is uncoupled from polymerization and occurs in a step that follows incorporation of a ATP-subunit in the polymer. Newly incorporated, slowly dissociating, terminal ATP-subunits form a stable cap at the ends of F-actin filaments. 

Pj release occurs at a relatively apparent slow rate (kobs = 0.005 s" ), so that the transient intermediate F-ADP-Pj in which P is non-covalently bound, has a life time of 2-3 minutes (Carlier and Pantaloni, 1986 Carlier, 1987). While the y-phosphate cleavage step is irreversible as assessed by 0 exchange studies (Carlier et al., 1987), the release of Pi is reversible. Binding of H2PO4 (Kp 10 M) causes the stabilization of actin filaments and the rate of filament growth varies linearly with the concentration of actin monomer in the presence of Pi (Carlier and Pantaloni, 1988). Therefore, Pi release appears as the elementary step responsible for the destabilization of actin-actin interactions in the filament. 

A critical factor for biotechnology application is the stability of the enzyme electrode. Hydrogenase immobilized into carbon filament material has high level of both operational and storage stability. Even after the half year of storage with periodical testing, the enzyme electrode preserved more than 50 % of its initial activity [9,10], Thus, it is possible to achieve appropriate stability of the enzyme electrode, suitable for hydrogen fuel cells development. 

Hydrolytic Stability. Hydrolytic stability of PET filaments obtained by the chain extender method was examined by holding the filaments at 150° C for six hours at 100 relative humidity. The results shown in Figure 11 indicate that the hydrolytic stability of PET decreases with increasing carboxyl content. 

Besides the electrical and thermal aspects, carbon conductive additives influence the mechanical properties of the electrodes. In particular, due to its compressibility, graphite improves the electrode density and mechanical stability. The generally lower DBPA of graphite is the reason for the lower amount of binder material necessary to achieve a suitable mechanical stability of the electrode. Further, a more facile spreadability of graphitic filaments in the electrode mass is reported for primary lithium cells.92... 

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