Protein , denaturation dissociation

Protein Subunit Dissociation-Association Volumes and Protein Denaturation Volumes ... 

Whey protein concentrates (WPC), which are relatively new forms of milk protein products available for emulsification uses, have also been studied (4,28,29). WPC products prepared by gel filtration, ultrafiltration, metaphosphate precipitation and carboxymethyl cellulose precipitation all exhibited inferior emulsification properties compared to caseinate, both in model systems and in a simulated whipped topping formulation (2. However, additional work is proceeding on this topic and it is expected that WPC will be found to be capable of providing reasonable functionality in the emulsification area, especially if proper processing conditions are followed to minimize protein denaturation during their production. Such adverse effects on the functionality of WPC are undoubtedly due to their Irreversible interaction during heating processes which impair their ability to dissociate and unfold at the emulsion interface in order to function as an emulsifier (22). 

Since food systems usually contain a heterogeneous mixture of proteins and polysaccharides differing in chemical nature, conformation, chain rigidity, size, and shape of molecules, degrees of hydrolysis, denaturation, dissociation and aggregation, information on model systems containing two biopolymers is not sufficient to interpret phase behaviour and functionality of real dispersed food systems. 

This review deals first (Part II) with recent work on the acid-base dissociations of native proteins. This is followed (Part III) by a discussion of unreactive prototropic groups in certain native proteins, with emphasis on conditions for their detection, and their relation to protein denaturation and the structural changes which accompany it. 

The effect of other protein denaturants on subunit dissociation has also been studied. Thus 10M urea did not dissociate apoferritin (109) and produced no change in the optical rotatory properties of ferritin and apoferritin (158). However, 10 M urea did produce a considerable... 

In the most powerful technique for resolving protein mixtures, proteins are exposed to the ionic detergent SDS (sodium dodecylsulfate) before and during gel electrophoresis (Figure 3-32). SDS denatures proteins, causing multimeric proteins to dissociate into their subunits, and all polypeptide chains are forced into extended conformations with similar charge mass ratios. SDS treatment thus... 

Since hydrogen bonds are relatively weak (1-5 kcal/mole) they can be easily dissociated, even by warming. The secondary and tertiary structure of enzymes (and other proteins) can be thermally unravelled, leading to destruction of catalytic activity. This protein denaturing process can also be brought about by chemical means such as with urea. 

Gupta [ref. 71] reported a method, based on SEC with TSKgel G3000SW, used to separate and quantify the individual milk proteins of native and/or denatured forms. The eluent used for whey proteins was a 0.1 M phosphate buffer, containing 0.05 M NaCl and 0.02 % sodium azide (pH 6.8). The denatured proteins were dissociated into their monomer units by SDS and 2 mercaptoethanol and separated with a 0.1 M phosphate buffer containing 0.1 % SDS. 

Acid-soluble sugars, phosphates, nucleotides, and phospholipids are usually removed by taking advantage of the acid and alcohol insolubility of nucleic acids and nucleoproteins. Protein removal or elimination may be accomplished in three ways (1) acid hydrolyms of the nucleic acids to acid-soluble components without protein hydrolysis (S) hydrolysis of protein phosphorus to inorganic phosphorus and of RNA to acid-soluble mononucleotides by alki and (S) dissociation of nucleic acid from protein by salt extraction followed by protein denaturation. The separation of the two types of nucleic acids from each other, which is required in any case depending on ultraviolet spectrophotometry or phosphate analysis, is... 

Sodium dodecyl sulphate is bound co-operatively to most protein, the critical concentration for co-operative binding being about 25 % of the CMC. Non-ionic surfactants and the bile salts do not usually induce co-operative binding and do not usually, therefore, denature proteins, although dissociation into inactive or... 

Zn, or a more complex organic or organometaUic molecule called a coenzyme. The catalytic activity provided by enzymes allows for much lower limits of detection than would be obtained with common binding techniques. As expected, the catalytic activity of enzymes depends upon the integrity of their native protein conformation. If an enzyme is denatured, dissociated into its subunits, or broken down into its component amino acids, its catalytic activity is destroyed. Enzyme-coupled receptors can also be used to modify the recognition mechanisms. For instance, the activity of an enzyme can be modulated when a ligand binds at the receptor. This enzymatic activity is often gready enhanced by an enzyme cascade, which leads to complex reactions in the cell. 

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