Proteins chemical degradation

All proteins and peptides display chemical and physical instability that affects the way they are distributed and cleared in the body and their delivery to the site of action. Physical and chemical instability is affected by primary sequences and secondary and tertiary structures and the degree of glyco-sylation of protein. Chemical degradation of proteins and peptides involves deamidation, racemization, hydrolysis, oxidation, beta elimination, and disulfide exchange. Physical degradation of proteins involves denaturation and aggregation. 

DePaz R, Barnett CC, Dale DA, Carpenter JF, Gaertner AL, Randolph TW.The excluding effects of sucrose on a protein chemical degradation pathway methionine oxidation in subhUsin. Arch Biochem Biophys 2000 384 123-32. 

The duration of such toxicity tests varies. In the USA, the FDA usually recommends a period of up to 2 years, whereas in Europe the recommended duration is usually much shorter. Chronic toxicity studies of biopharmaceuticals can also be complicated by their likely stimulation of an immune response in the recipient animals. In the context of new chemical entities (NCEs, i.e. low molecular weight traditional chemicals), not only can the drug itself exhibit a toxic effect, but so potentially can drug breakdown products. As proteins are degraded to amino acids, any potentially toxicity associated with protein-based drugs is typically associated with the protein itself and not degradation products. 

Extensive biochemical and spectroscopic studies have been undertaken on hCP in order to investigate the nature of the copper centers and their role in structure-function relationships. However, the protein is very susceptible to aggregation, proteolysis, loss of copper, and other chemical degradations and requires careful preparation and handling in these circumstances it is difficult to review all the literature objectively and comprehensively. A three-dimensional crystal structure of hCP has been reported at a nominal resolution of 3.1A [7], but this resolution has been extended to just beyond 3.0 A. This chapter will summarize some of the more important biochemical and spectroscopic studies of the protein. It will then focus on the structural results recently obtained by X-ray crystallographic methods and attempt to explain putative functions of the protein in terms of its molecular structure. 

Even when hydrolysis and epimerization can be avoided during sample preparation and handling, it is not possible to conclude definitively whether the compounds found in plasma and urine are true metabolites or simply degradation products. Indeed, chemical degradation can also occur within the body since urine and plasma contain a wide variety of potential catalysts, including metal ions, phosphate ions, proteins, and sugars (see Sect. 5.2.6). Whereas the existence of mammalian enzymes that act on penicillins and cephalosporins is considered possible [155], no such mammalian enzyme appears to have been identified to date. 

K. Patel, R. T. Borchardt, Deamidation of Asparaginyl Residues in Proteins A Potential Pathway for Chemical Degradation of Proteins in Lyophihzed Dosage Form , J. Parent. Sci. Technol. 1990,44, 300-301. 

Roles of Iron—Sulfur Proteins in Degradation of Pesticidal Chemicals by Microorganisms... 

The stepwise chemical degradation of peptide chains with Edman s method represents one of the truly significant additions to the inventory of methods in modem biochemistry. Without this procedure the rapid development within recent years of our knowledge about stmcture and function of proteins would have been impossible (see Attempts based on different chemical reactions have not yet yielded practical methods 56-62)... 

In general, transition metal ions are undesired in protein formulations because they can catalyze physical and chemical degradation reactions in proteins. However, specific metal ions are included in formulations when they are cofactors to proteins and in suspension formulations of proteins where they form coordination complexes (e.g., zinc suspension of insulin). Recently, the use of magnesium ions (10-120 mM) has been proposed to inhibit the isomerization of aspartic acid to isoaspartic acid (63). 

The protein-chemical characterisation revealed a homotetrameric enzyme with a molecular mass of 362 kDa, an isoelectric point of pi 6.16 and a blocked N-terminus in Edman degradation studies [353], In biochemical studies we investigated the effect of free and chelated first-row transition metal ions (Cu2+, Ni2+, Zn2+ and Co2+) on SuSy activity [355]. Further experiments on the binding behaviour of SuSy in immobilized metal ion affinity chromatography (I MAC) gave an insight into the topography of sucrose synthase from rice... 

Individual flavor components are subjected to losses through distillation, flavor binding by starches and proteins, and chemical degradation during the microwave process. Specific data on flavor loss by distillation as affected by the various media and chemical modification of flavor precursors is presented in this paper. Data on flavor binding during microwave processing is addressed in a subsequent paper. 

Burdon542 has surveyed the current hypotheses for the structure of humic substances and has concluded that the various products from chemical degradations and NMR data are all consistent with their being mixtures of plant and microbial materials and their microbial degradation products. The examination of soil carbohydrates, proteins, lipids, and aromatics supported this view the presence of colour, fluorescence, ESR signals, mellitic acid, and other features do not contradict it. Regarding the Maillard reaction, some free monosaccharides and the necessary amino species are present in soil, so it may proceed, but only to a small extent it is not a major process. However, in marine environments, the relative abundance of carbohydrates and proteins makes them more probable precursors of humic substances than lignin or polyphenols. 

The primary structure (i.e., the amino acid sequence) of a protein can be determined by stepwise chemical degradation of the purified protein. By far the most powerful and commonly used technique for doing this is the automated Edman degradation. The amino terminal amino acid residue of the polypeptide is reacted with Edman s reagent (phenylisothiocyanate) to form the phenylthiocar-bamyl derivative, which is removed without hydrolysis of the other peptide bonds by cyclization in anhydrous acid. The amino acid derivative is converted to the more stable phenylthiohydantoin and identified by HPLC. The process can be repeated many times, removing the amino acids from the amino terminus of the polypeptide one residue at a time and identifying them until the entire sequence... 

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