Partial or Complete Degradation

Enzymes, like other cellular proteins, are completely degraded to their constituent amino acids via the proteolytic sequence. There is no evidence that peptides which might occur as breakdown products can be utilized for the synthesis of the same or different proteins—another way of stating that protein degradation and protein synthesis do not share any intermediates. However, this does not mean that proteolytic cleavage necessarily leads to loss of function, nor the converse that activity is always retained unless proteolytic hydrolysis has occurred. 

With some enzymes, the cleavage of one or more internal peptide bonds does not cause protein disruption and can in fact lead to an increase in enzyme activity. This occurs not only during the processing of proenzymes, such as the conversion of trypsinogen to trypsin or chy-motrypsinogen to chymotrypsin, but also with intracellular enzymes such as hepatic fructose bisphosphatase (Pontremoli et al., 1973). This enzyme does not fall apart upon limited proteolytic cleavage, because 

In general, the initiation of proteolysis can be expected to lead rapidly to complete degradation of the enzyme to amino acids. Nicking is perhaps best considered as an irreversible posttranslational modification that bears some similarities to methylation or phosphorylation of amino acids in proteins. It is doubtful whether it occurs with many enzymes. 

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Halogenated aliphatics can be partially or completely degraded under anaerobic conditions through a transformation reaction called reductive de-halogenation. Often a co-metabolic degradation step, reductive dehalogenation... 

Bacteria interact with environmental chemicals in a number of ways. Many organic compounds are partially or completely degraded by bacteria. In some cases the organic products are even more toxic than the original pollutants. 

Although the possibility of bioremediation of sites contaminated with nitrotoluene waste is clearly possible, important issues should be clearly appreciated. These include (a) additional carbon sources may be necessary to accomplish partial or complete reduction of nitro groups, (b) under aerobic conditions, dimeric azo compounds may be formed as terminal metabolites, and (c) aromatic amines may be incorporated into humic material by covalent bonding and thereby resist further degradation. 

One of the primary mechanisms of protein degradation is the loss of globular structure [118, 119]. This process, termed denaturation, leads to a partially or completely unfolded species which usually lacks any of the biological activity of the native protein. A variety of methods have been employed to monitor the denaturation of proteins, including fluorescence, infrared, nuclear magnetic resonance (NMR), and CD spectroscopy. As CD is very sensitive to changes in both secondary and tertiary structure, its application to the study of protein folding... 

In H2 production from methane, carbon formation usually takes place in the form of fibres or whiskers, with a small Ni particle at the top of a fibre.5,6 Carbon formation may lead to the breakdown of the catalyst, and carbon deposits and degraded catalyst may cause partial or complete blockage of the reformer tubes. Uneven flow distribution is responsible for localised overheating of the hot tubes. Accordingly, carbon formation must be avoided in tubular reformers. There are two major reactions responsible for carbon formation ... 

From an environmental point of view, it therefore appears that the complete degradation of chlorinated alkenes and alkanes will often require the operation of both anaerobic and aerobic steps for example, partial or complete dehalogenation may occur under anaerobic conditions, and aerobic degradation of the partially dechlorinated metabolites such as dichlo-romethane (La Roche and Leisinger 1991) and vinyl chloride (Castro et al. 1992a,b Hartmans and de Bont 1992) may then subsequently take place. The combination of the two activities in a single strain has been exploited in the genetically constructed strain of P. putida and has been discussed above. 

The resulting polymers = 0.10-0.24 dl/g) show a partial or complete solubility in m-cresol and NMP. The silicon content in PNI was dependent on the diamine structure, and with an increase in the silicon content, the polymer solubility was improved. For the thermal stability, the reverse trend was observed, namely as the silicon content in the polymer increased, the temperature of PNI degradation decreased and varied in the 455-475 °C range. 

It is clear that a sharp Curie tenperature cannot be defined for relaxor materials in the same way as for simple materials such as BaTiOj. To take account of this, a depolarisation temperature, is taken as the temperature at which a partial or complete loss of polarisation, and a consequent degradation in piezoelectric performance, occurs. In materials with relative permittivity behaviour similar to that in Figure 6.18b,... 

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