Post-processing modification

As a final comment, the self-passivation response is not only advantageous for enhancing durability in service, but also provides unique opportunities for post-processing modification of nanocomposites. For example, pretreatment of the nanocomposite in oxygen plasma may enhance the materials resistance to thermal-oxidative or UV-electron environments. Alternatively, self-generation of the inorganic surface on commercial nanocomposites films may enhanced barrier properties before introduction to service. 

After the needed sections are generated, the resulting cross-section data is stored in the 3D CAD structure during post-processing. Modification of resulting cross section geometry is based on classification rules structure, geometrical sets, properties, line type, line thickness and line color. 

According to the modification that occurred before or after polymer material molding, modifications can be divided into the categories of polymer synthesis modification, processing modification, and post-processing modification. 

MammaBan. For mammalian proteins, mammalian cells offer the most natural host for expression. Problems of incorrect processing and post-translational modification are avoided using these cells. Mammalian cells are usually grown in continuous cell culture, reducing the variabiUty in results (see Cell CULTURE technology). Moderate-level production of native protein is possible. The procedure, however, is slow and very cosdy, and the level of protein expression is low. Thus large-scale production of proteins in mammalian cells is not practical. When low quantities of protein are sufficient, this system offers the several advantages described. 

After their synthesis (translation), most proteins go through a maturation process, called post-translational modification that affects their activity. One common post-translational modification of proteins is phosphorylation. Two functional classes of enzymes mediate this reversible process protein kinases add phosphate groups to hydroxyl groups of serine, threonine and tyrosine in their substrate, while protein phosphatases remove phosphate groups. The phosphate-linking... 

Proteosomal degration is the process by which improperly folded proteins or proteins with altered post-translational modifications are removed from a cell before they have a detrimental effect on cellular function. This is performed in small organelles known as proteosomes. Proteins are targeted for destruction in the proteosome by having a number of small ubiquitin molecules added. 

When recombinant proteins are produced in a heterologous system, there may potentially be differences between the final product and the natural molecule. Hence, for each new protein produced in alfalfa, a thorough analysis of the processing, folding, assembly and post-translational modification is conducted to ensure the conformity of the purified molecules. This section describes the analysis of alfalfa-derived... 

Plant-based production systems are now being used commercially for the synthesis of foreign proteins [1-3]. Post-translational modification in plant cells is similar to that carried out by animal cells plant cells are also able to fold multimeric proteins correctly. The sites of glycosylation on plant-produced mammalian proteins are the same as on the native protein however, processing of N-linked glycans in the secretory pathway of plant cells results in a more diverse array of glycoforms than is produced in animal expression systems [4]. Glycoprotein activity is retained in plant-derived mammalian proteins. 

One of the most important considerations for the improvement of protein yields is subcellular protein targeting, because the compartment in which a recombinant protein accumulates strongly influences the interrelated processes of folding, assembly and post-translational modification. All of these contribute to protein stability and hence help to determine the final yield [88]. 

In addition to the 20 common amino acids, some modified amino acids are also found in several proteins. These amino acids are normally altered via a process of post-translational modification (PTM) reactions (i.e. modified after protein synthesis is complete). Almost 200 such modified amino acids have been characterized to date. The more common such modifications are discussed separately in Section 2.5. 

As secretory vesicles mature, many secretory polypeptides undergo post-translational modifications. Many hormones and neuropeptides as well as hydrolytic enzymes are synthesized as inactive polypeptide precursors that need to undergo proteolysis to become active. This maturation process usually starts in the TGN and continues in the secretory vesicles, but may be completed in the extracellular space soon after exocytosis takes place in some cases. The maturation process for neuropeptides is described in Chapter 18. 

Neuropeptides are packaged into large, dense-core vesicles 325 Diversity is generated by families of propeptides, alternative splicing, proteolytic processing and post-translational modifications 326... 

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