Sequential Degradation

Edman degradation. Sequential degradation of peptides beginning at the iV-tenninal residue based on the reaction of phenylisocyanate with the a-amino group of the terminal amino acid of the peptide chain. 

The compound was quite obviously an amine due to its basic character. Von Braun degradation (NMe - NCN) and Hofmann degradation (sequential methylation -elimination) implied a cyclic tertiary amine. Further exhaustive Hofmann degradation led to an unusual net elimination of both trimethylamine and ethylene. (This reaction was driven by aromatization of the C-ring after elimination of the Q5-C16-N17 ethylamine bridge). 

Material balances by Kim and Sartori (1984) indicated that a fourth degradation product, presumably a polymeric material, which was not detectable by gas chromatography, began to form about the same time as BHEP. These observations led Kim and Sartori to suggest that DEA degrades sequentially to HEO, TH D, BHEP, and finally to polymeric degradation products. These polymeric degradation products were identified in further studies by Hsu and Kim (1985). 

The thermal degradation of mixtures of the common automotive plastics polypropylene, ABS, PVC, and polyurethane can produce low molecular weight chemicals (57). Composition of the blend affected reaction rates. Sequential thermolysis and gasification of commingled plastics found in other waste streams to produce a syngas containing primarily carbon monoxide and hydrogen has been reported (58). 

Extraction of hemiceUulose is a complex process that alters or degrades hemiceUulose in some manner (11,138). Alkaline reagents that break hydrogen bonds are the most effective solvents but they de-estetify and initiate -elimination reactions. Polar solvents such as DMSO and dimethylformamide are more specific and are used to extract partiaUy acetylated polymers from milled wood or holoceUulose (11,139). Solvent mixtures of increasing solvent power are employed in a sequential manner (138) and advantage is taken of the different behavior of various alkaUes and alkaline complexes under different experimental conditions of extraction, concentration, and temperature (4,140). Some sequences for these elaborate extraction schemes have been summarized (138,139) and an experimenter should optimize them for the material involved and the desired end product (102). 

Substitution of alkaline cyanates by isocyanates allows the preparation of 3-substituted hydantoias, both from amino acids (64) and amino nitriles (65). The related reaction between a-amino acids and phenyl isothiocyanate to yield 5-substituted 3-phenyl-2-thiohydantoiQS has been used for the analytical characterization of amino acids, and is the basis of the Edman method for the sequential degradation of peptides with concomitant identification of the /V-terminal amino acid. 

The explanation proposed involved sequential inter- and intramolecular addition steps. The presence of cyclic structures within the polymer chain was soon confirmed by degradation experiments.106 However, these experiments did... 

The GAGs are synthesized by the sequential actions of a battery of specific enzymes (glycosyltransferases, epimerases, suhotransferases, etc) and are degraded by the sequential action of lysosomal hydrolases. Genetic deficiencies of the latter result in mucopolysaccharidoses (eg, Hurler syndrome). 

In Fig. 4 we compare the timings for three different models, the simple one K per processor, the wrapped algorithm, and a model where two states are assigned per processor sequentially. Note that until J = 50 the one K per processor model job uses the smallest amount of wall clock time. It is clear, however, that this method does not make efficient use of computer resources. The wrapped model, however, scales very well and outperforms the sequential two K per processor model at every / > 0, a clear illustration of the degradation of performance due to load imbalance. 

Because of their very complex chemical structures and heterogeneity, melanins are difficult to extract, separate, and characterize from tissues. Eumelanins are insoluble in water and organic solvents. They can be extracted from tissues with strong chemicals that are capable of removing lipids, proteins, and other tissue components but also lead to the formation of degradation products. Enzymatic procedures were developed for the isolation of eumelanins from mammalian hair and irises. The first step is sequential digestion with protease, proteinase K, and papaine in the presence... 

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