Degradation Chamber Research Articles

Bio- and Photo-degradation of Natural Fiber Reinforced Starch-based Biocomposites

Biocomposites of starch and natural fibers were produced by compression molding. Potato, sweet potato, and corn starch were used as matrices of the biocomposites. Natural fibers including jute, sisal, and cabuya were used as discrete reinforcement. Water, glycerol, glycols, and a chitosan solution were used as plasticizers. Biodegradation was studied using both a compost chamber and a spore solution in an agar-based culture medium. Weight loss was recorded at specific time intervals for the tests of biodegradation in a compost chamber. Microscopical analysis was used to assess biodegradation in agar medium. Photodegradation was studied in a UV degradation chamber. Weight loss was also recorded at specific time intervals. All the biocomposites displayed similar degradation patterns under compost. During the first seven days a marked water absorption tendency was dominant in the weight variation curves. After that period, weight loss became more evident. In the case of UV degradation, a large part of the recorded weight loss was due to a drying effect due to IR radiation and took place mainly during the first seven days. This was taken into account in order to determine the net effect of UV degradation on weight loss.

The tmRNA system for ribosome rescue and targeted protein degradation.

Stalled bacterial ribosomes are recognized and rescued by the tmRNA/SmpB system, resulting in addition of an 11-residue ssrA tag at the C-terminus of the protein being synthesized. This ssrA-tagged protein is subsequently degraded by energy-dependent cytoplasmic proteases. A specialized adaptor protein (SspB) binds ssrA-tagged proteins and delivers them to the ClpXP protease for degradation. ClpX is an ATP-fueled hexameric machine that binds to the ssrA tag, denatures the attached protein if necessary, and then translocates the denatured polypeptide through a central pore and into the degradation chamber of ClpP, a barrel-shaped peptidase for proteolysis. Studies of the mechanisms of tag-mediated and adaptor-mediated substrate recognition allowed us to design a modified ssrA tag and to engineer a system that permits controlled SspB-dependent protein degradation of any suitably tagged bacterial protein. ClpX is a member of the AAA+ ATPase family. As a group, the enzymes use ATP hydrolysis to power the mechanical denaturation, disassembly, and transport of macromolecules. We designed single-chain “hexamers” of ClpX, allowing the functional roles of individual subunits within the ring to be dissected. These studies rule out concerted and strict sequential models of ATP hydrolysis and suggest that a probabilistic mechanism is used to translocate denatured polypeptides despite radically different sequences and physical properties. These studies have important implications for protein-quality control and for the mechanisms of AAA+ molecular machines.

Partitioning between unfolding and release of native domains during ClpXP degradation determines substrate selectivity and partial processing

Energy-dependent proteases, such as ClpXP, are responsible for the regulated destruction of proteins in all cells. AAA+ ATPases in these proteases bind protein substrates and power their mechanical denaturation and subsequent translocation into a secluded degradation chamber where polypeptide cleavage occurs. Here, we show that model unfolded substrates are engaged rapidly by ClpXP and are then spooled into the degradation chamber at a rate proportional to their length. Degradation and competition studies indicate that ClpXP initially binds native and unfolded substrates similarly. However, stable native substrates then partition between frequent release and infrequent denaturation, with only the latter step resulting in committed degradation. During degradation of a fusion protein with three tandem native domains, partially degraded species with one and two intact domains accumulated. These processed proteins were not bound to the enzyme, showing that release can occur even after translocation and degradation of a substrate have commenced. The release of stable substrates and committed engagement of denatured or unstable native molecules ensures that ClpXP degrades less stable substrates in a population preferentially. This mechanism prevents trapping of the enzyme in futile degradation attempts and ensures that the energy of ATP hydrolysis is used efficiently for protein degradation.

Communication between ClpX and ClpP during substrate processing and degradation.

In the ClpXP compartmental protease, ring hexamers of the AAA(+) ClpX ATPase bind, denature and then translocate protein substrates into the degradation chamber of the double-ring ClpP(14) peptidase. A key question is the extent to which functional communication between ClpX and ClpP occurs and is regulated during substrate processing. Here, we show that ClpX-ClpP affinity varies with the protein-processing task of ClpX and with the catalytic engagement of the active sites of ClpP. Functional communication between symmetry-mismatched ClpXP rings depends on the ATPase activity of ClpX and seems to be transmitted through structural changes in its IGF loops, which contact ClpP. A conserved arginine in the sensor II helix of ClpX links the nucleotide state of ClpX to the binding of ClpP and protein substrates. A simple model explains the observed relationships between ATP binding, ATP hydrolysis and functional interactions between ClpX, protein substrates and ClpP.

The effect of titanium dioxide alumina beads on the photocatalytic degradation of picloram in water.

Photocatalytic degradation of pesticides with titanium dioxide (TiO(2)) and other catalysts has shown promise as a potential water remediation method. Titanium-based powders have been used in photocatalytic degradation studies but have limitations. The objective of this study was to determine picloram degradation in water using various UV light sources and low-pressure metal organic chemical vapor deposition titanium dioxide alumina beads (TDABs) as a catalyst. A triple-annular, flow-through photoreactor was used as a degradation chamber. A picloram test solution of 50 microg/mL was introduced to the photoreactor inlet and recycled for 10 h at a flow rate of 50 mL/min. Three ultraviolet light sources were compared for their photocatalytic capacity (UV-A, UV-B, and UV-C) both with and without TDABs. TDABs were added to the photoreactor at 1.8 g/cm(3). Dark treatments with and without TDABs were included to quantify hydrolysis or adsorption. A 500-microL aliquot was taken from the test solution 14 times during the 10-h recycling period. Sampling times ranged from 0 to 600 min (10 h). These aliquots were placed in a vial and analyzed by high performance liquid chromatography equipped with a photodiode array detector. Picloram was not significantly hydrolyzed or adsorbed to TDABs during the experiment. The picloram degradation rate with UV-A and TDABs (t(1/2) = 119.5 min) was greater than the degradation rate of UV-A alone (t(1/2)=2288 min). Picloram degradation was not enhanced by the presence of TDABs with either UV-B or UV-C. This may be attributed to inadequate TDAB densities and/or poor light penetration in the photoreactor. Rapid picloram degradation occurred with both UV-B and UV-C, regardless of the presence of TDABs with mean half-lives ranging from 7 to 18 min. These rates were 8 to 16 times faster than picloram degradation using UV-A with TDABs. TDABs' greatest photocatalytic effect was with the lowest energy light source (UV-A). However, picloram degradation was not enhanced when TDABs were combined with more powerful, shorter wavelength light.

Degradation kinetics of meta‐ and para‐aromatic polyamides

AbstractPoly(m‐phenylenediamineisophthal)amide (MPD‐I) and poly(p‐phenylenediamineterephthal)amide (PPD‐T) are among the most important high‐tech polymers. The degradation of three MPD‐I fibers with different molecular weight distributions and a PPD‐T fiber was studied in a proprietary laboratory degradation chamber. The results were fitted satisfactorily to a kinetic model describing the degradation as a combination of thermal scission, oxidation, and hydrolysis. PPD‐T degradation is slower than that of MPD‐I, and MPD‐I resistance to degradation increases as polydispersity decreases. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 15–21, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10031