Enzymatic modifications types

Mode of action Activation of macrophages/monocytes release of endogenous mediators such as lipids from arachidonic acid, reduced oxygen species, proteins 1. Pore formation in cell membranes 2. Enzymatic modification of specific substrates in the cytosol of host cells (AB-type toxins) 3. Superantigen stimulation of the immune system... 

In addition to the 20 proteinogenic amino acids (see p. 60), there are also many more compounds of the same type in nature. These arise during metabolic reactions (A) or as a result of enzymatic modifications of amino acid residues in peptides or proteins (B). The biogenic amines (C) are synthesized from a-amino acids by decarboxylation. 

Most readers will probably agree that there have been extensive advances in the fundamental areas of chemical and enzymatic modifications. The organizers do not expect similar agreements as to the success of the application of these methods in food, nutrition, and pharmacological areas. This lack of agreement would be particularly evident for the eventual adoption of some methods for human use. Perhaps it will be evident, however, that fundamental studies will show what types of materials are required for human use and that, after proper research into the health and safety aspects, eventually some of these methods will be applied for human use. 

Cytokinin specificity is determined by the structure of its side chain, where even a small modification can significantly affects the biological activity. Among enzymatic modifications that have been already proved in vivo are ranked O-glycosylation and O-acetylation of zeatin, cisJtrans isomerization of its hydroxyl group, double bond reduction to dihydrozeatin and hydroxylation of A -isopentenyl moiety of isopentenyladenine type to zeatin-types of cytokinins. 

Membrane processes have a potential application within many areas of industrial enzymatic hydrolysis of proteins. Table 1 shows how membrane processes can be applied in the different types of enzymatic modification of protein. Thus membrane processes may be used for pre-treatment of proteins, for the reaction step and as an essential part of the purification or posttreatment step. 

A proteinase-catalyzed reaction including splitting and synthesis of peptide bonds is a process also suitable for covalent amino acid incorporation into peptide chains. This type of enzymatic modification reaction of food proteins is useful for different purposes alteration of sensory properties, solubility, nutritional quality, functional properties, antifreeze character, and different biological activities. Recently, special proteinase-catalyzed reactions have been elaborated by which proteins can be modified with particular respect to their primary structure and conformation. 

Enzymatic modification of proteins has been elaborated also for desired modifications of functional properties of food proteins. The surface properties of a functional protein can radically change when the protein associates with other types of molecules possessing surfactant properties. The versatility of proteins is mainly due to their complex structure, and the variability of functional properties of proteins can be ascribed to differences in the structure of protein molecules, more exactly to varieties of their building amino acids [11], The most important properties like surface activity and proteolytic degradability are basically influenced by compositional and structural features [129], Enzymatic modification of food proteins may alter their charge... 

Practically all types of enzymatic modifications of peptides and proteins are suitable processes for modification of viscoelastic [140]... 

The conversion of cellulase component B into A may be a result of some enzymatic modification of the enzyme molecule. Similar type of in vitro conversion has also been reported, for example, for the extracellular cellulase of Trichoderma viride (38) and the cell-bound invertase of bakers yeast (15). The occurrence of another type of conversion where the reversible association and dissociation of active subunits are operative, has been proven on the intrawall and extracellular invertases of Neurospora crassa (25). 

It is often difficult to establish that a recombinant protein manufactured in a novel cell system by genetically engineered approaches has the same tertiary structure as the authentic wild-type protein. Because detection by spectroscopic techniques such as circular dichroism (CD) of subtle conformational differences that may arise due to minor perturbations in the hydrophobic regions of a protein is often difficult, the observation of identical retention times for the rDNA and the wild-type protein by RPC and HIC procedures is a useful indicator of common three-dimensional structures. Moreover, when small structural variations arise due to amino acid residue additions, replacement, or chemical/enzymatic modifications, the use of RPC and HIC procedures under less denaturing elution conditions often favors the resolution of these species from the parent protein. The separation of recombinant Met -hGH from recombinant hGH is an example [385,404,415] where such approaches have been successfully applied. 

This enzymatic modification of chitosan was applied for the synthesis of a chitosan-catechin conjugate. The formation of a Michael-type adduct and/or Schiff base was proposed during the PPO-catalyzed conjugation of catechin with chitosan [60]. Rheological measurement demonstrates that the resulting conjugate behaves as an associative thickener. 

Two types of interesterification are presently in use chemical and enzymatic. Enzymatic modifications rely on the use of random or regiospecific (1,3-or 2-specific) and fatty acid-specific lipases as catalysts, whereas for chemical modifications metal alkali catalysts are usually employed. 

Process Va.ria.tlons. The conventional techniques for tea manufacture have been replaced in part by newer processing methods adopted for a greater degree of automation and control. These newer methods include withering modification (78), different types of maceration equipment (79), closed systems for fermentation (80), and fluid-bed dryers (81). A thermal process has been described which utilizes decreased time periods for enzymatic reactions but depends on heat treatment at 50—65°C to develop black tea character (82). It is claimed that tannin—protein complex formation is decreased and, therefore, greater tannin extractabiUty is achieved. Tea value is beheved to be increased through use of this process. 

Resistance to a range of antibiotics is of increasing concern in clinical practice since the genes are often carried on transmissible plasmids. There are different types of mechanism that confer resistance, inclnding enzymatic covalent modification of the antibiotic, effective efflnx systems, and indnction of a cellnlar enzyme that is resistant to the antibiotic. Examples of these are used as illustration. 

Not all modified starches are suitable for removal by aqueous dissolution alone. Such modifications of natural starches are carried out to reduce solution viscosity, to improve adhesion and ostensibly to enhance aqueous solubility. Commercial brands vary [169], however, from readily soluble types to those of limited solubility. Indeed, some may be as difficult to dissolve as potato starch if they have been overdried. It is thus very important to be sure of the properties of any modified starch present. If there are any doubts about aqueous dissolution, desizing should be carried out by enzymatic or oxidative treatment. Even if the size polymer is sufficiently soluble, it is important to ensure that the washing-off range is adequate. Whilst the above comments relate to modified starches, other size polymers such as poly(vinyl acetate/alcohol) and acrylic acid copolymers vary from brand to brand with regard to ease of dissolution. 

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