Proteins naturally occurring

Proteins - Naturally occurring and synthetic polypeptides having molecular weights greater than about 10,000 (the limit is not precise). See also Peptides. [5]... 

Quality markers Proteins Naturally occurring, species-specific process sensitive... 

Allergens Proteins Naturally occurring in nuts, fruits, gluten, eggs, milk, etc. 

PhOSphorylatGd Proteins. Naturally occurring phosphorus-containing proteins include such important examples as casein, discussed elsewhere in this Encyclopedia. In living organisms, proteins are often phosphorylated enzymatically on the serine or tyrosine hydroxyl group as an activation or regulation step, and over-phosphorylation may play a role in disease this biochemistry is outside the scope of the present article. 

Proteins, naturally occurring macromolecular surfactants with amphiphilic nature, are adsorbed onto interfaces, thereby affecting the physical states of interfaces. Many enzymes are involved in catalytic reaction at interfaces. For enzymatic reaction at interfaces, different from the reaction in homogeneous systems, interfacial contact and subsequent conformational change of enzymes are important events determining their catalytic activity. In this chapter, I will describe the conformation of proteins and their interaction (protein-protein and protein-surfactant) at interfaces (mainly liquid-liquid interfaces). The characteristics of enzymatic reaction at liquid-liquid and solid-liquid interfaces, especially lipase reaction, wiU also be described. 

Chitin is the second most abundant organic compound in nature after cellulose. It is found mainly in the animal kingdom, where it is the main structural polysaccharide in the exoskeleton (shells) of crustaceans, insects and other invertebrates. It also occurs in some algae, fimgi, yeasts and bacteria, usually associated with proteins. Naturally occurring chitin is consumed only rarely. Some beetles and sea foods with shells (such as crabs and snails) are eaten as delicacies, and are largely made of chitin. The chitin content in the exoskeleton of crabs is 61-77%. 

M.p. 207°C. The naturally occurring substance is dextrorotatory. Arginine is one of the essential amino-acids and one of the most widely distributed products of protein hydrolysis. It is obtained in particularly high concentration from proteins belonging to the prolamine and histone classes. It plays an important role in the production of urea as an excretory product. 

The naturally occurring substance is L-aspartic acid. One of the acidic-amino acids obtained by the hydrolysis of proteins. 

CfiHqNaO . M.p. 277 C. The naturally occurring substance is laevorotatory. Histidine is one of the basic amino-acids occurring in the hydrolysis products of proteins, and particularly of the basic proteins, the protamines and histones. It is an essential constituent of the food of animals. 

C(,Hi3N02, CH3 CH2-CHMe-CHNH2-COOH. Colourless crystals, m.p. 284 C (decomp.). The naturally occurring substance is dextrorotatory. An amino-acid, occurring with leucine as a product of protein hydroly-... 

Most reactions in cells are carried out by enzymes [1], In many instances the rates of enzyme-catalysed reactions are enhanced by a factor of a million. A significantly large fraction of all known enzymes are proteins which are made from twenty naturally occurring amino acids. The amino acids are linked by peptide bonds to fonn polypeptide chains. The primary sequence of a protein specifies the linear order in which the amino acids are linked. To carry out the catalytic activity the linear sequence has to fold to a well defined tliree-dimensional (3D) stmcture. In cells only a relatively small fraction of proteins require assistance from chaperones (helper proteins) [2]. Even in the complicated cellular environment most proteins fold spontaneously upon synthesis. The detennination of the 3D folded stmcture from the one-dimensional primary sequence is the most popular protein folding problem. 

Naturally occurring molecular ensembles such as proteins from photosyntlietic systems (plants, algae, photosyntlietic bacteria, etc) are usually relatively rigid systems tliat contain various cliromophores and hold tliem at fixed positions and orientations relative to each otlier. That is why, despite tire numerous energy jumps between tire cliromophores, tlie resulting emitted fluorescence is polarized. The extent of tliis polarization tlius affords invaluable infonnation about tlie internal stmcture of molecular complexes. 

The most ambitious approaches to the protein folding problem attempt to solve it from firs principles (ab initio). As such, the problem is to explore the coirformational space of th molecule in order to identify the most appropriate structure. The total number of possibl conformations is invariably very large and so it is usual to try to find only the very lowes energy structure(s). Some form of empirical force field is usually used, often augmente with a solvation term (see Section 11.12). The global minimum in the energy function i assumed to correspond to the naturally occurring structure of the molecule. 

Lipids differ from the other classes of naturally occurring biomolecules (carbohy drates proteins and nucleic acids) in that they are more soluble m nonpolar to weakly polar solvents (diethyl ether hexane dichloromethane) than they are m water They include a variety of structural types a collection of which is introduced m this chapter... 

Polyamide (Section 20 17) A polymer in which individual structural units are joined by amide bonds Nylon is a syn thetic polyamide proteins are naturally occurring polyamides... 

Investigations have focused on the content of polyphenoHcs, tannins, and related compounds in various foods and the influence on nutrient availabiHty and protein digestibiHty. It has been estabHshed that naturally occurring concentrations of polyphenoloxidase and polyphenols in products such as mushrooms can result in reduced iron bio availabiHty (75). Likewise, several studies have focused on decreased protein digestibiHty caused by the tannins of common beans and rapeseed (canola) (76—78). 

Defatted peanuts are high in protein, low in moisture, contain only 20% of the naturally occurring fat, and have better stability than whole peanuts. Monosodium glutamate (MSG) has been used as a flavor enhancer for defatted nuts, but the result has not been entirely satisfactory as the addition of MSG produces a meaty rather than nutty flavor. This meaty flavor is more compatible with salted butter and nuts than with candy. 

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