Physical and Chemical Properties of Proteins

Physical and Chemical Properties of Proteins Physical Properties 

Denaturation of protein - The comparatively weak forces responsible for maintaining secondary, tertiary and quaternary structure of proteins are readily disrupted with resulting loss of biological activity. This disruption of native structure is termed denaturation. 

Physical and chemical factors are involved in the denaturation of protein  

Renaturation - Renaturation refers to the attainment of an original, regular three-dimensional functional protein after its denaturation. 

When active pancreatic ribonuclease A is treated with 8M urea or P-mercaptoethanol, it is converted to an inactive, denatured molecule. When urea or mercaptoethanol is removed, it attains its native (active) conformation. 

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The amide functionality plays an important role in the physical and chemical properties of proteins and peptides, especially in their ability to be involved in the photoinduced electron transfer process. Polyamides and proteins are known to take part in the biological electron transport mechanism for oxidation-reduction and photosynthesis processes. Therefore studies of the photochemistry of proteins or peptides are very important. Irradiation (at 254 nm) of the simplest dipeptide, glycylglycine, in aqueous solution affords carbon dioxide, ammonia and acetamide in relatively high yields and quantum yield (0.44)202 (equation 147). The reaction mechanism is thought to involve an electron transfer process. The isolation of intermediates such as IV-hydroxymethylacetamide and 7V-glycylglycyl-methyl acetamide confirmed the electron-transfer initiated free radical processes203 (equation 148). 

These data demonstrate that changes in foam properties of liquid cyclone processed cottonseed flour are inducible by treatment with succinic anhydride. Gel electrophoretic and solubility data show that there are alterations in the physical and chemical properties of proteins, and in certain cases these changes improve foam properties, that is, improve solubility and polypeptide dissociation of proteins at the interface of the foaming solution. Similar results have been reported for succinylated soybean and sunflower seed proteins (44. 46). 

V. Physical and Chemical Properties of Proteins in Nonaqueous Solvents. 59... 

In most proteins the sheets pack together in one of a small number of ways. The connections between secondary structures obey a set of empirical topological rules in almost all cases.. . Subsequently, it was argued that these similarities arise from the intrinsic physical and chemical properties of proteins, and a great deal of work was carried out to demonstrate that this is the case [emphasis added]. 

The 20 different R groups of amino acids are important factors in determining the physical and chemical properties of proteins that contain the amino acids. Acid-base behavior is... 

Many physical and chemical properties of proteins can be modified to enhance their surface activity. Some of the most important characteristics, such as surface film strength, viscoelasticity, and colloid stability, can be changed by extrinsic changes (pH, ionic strength, temperature, etc.), and others such as hydropho-bicity, flexibility of the polymer, and net charge can be altered by affecting the intrinsic properties of the protein (chemical or enzymatic modifications). The chemical modification of proteins will affect both protein-protein interactions and the interactions of protein with other surfactants. 

Other actions of estrogen include fluid retention, protein anabolism, thinning of the cervical mucus, and the inhibition or facilitation of ovulation. Estrogens contribute to the conservation of calcium and phosphorus, the growth of pubic and axillary hair, and pigmentation of the breast nipples and genitals. Estrogens also stimulate contraction of the fallopian tubes (which promotes movement of the ovum), modify the physical and chemical properties of the cervical mucus, and restore the endometrium after menstruation. 

Unlike the photosynthetic apparatus of photosynthetic bacteria, that of cyanobacteria consits of two photosystems, PS I and II, connected by an electron transport chain. The only chlorophyll present is chlorophyll a, and, therefore, chlorophylls b—d are not of interest in this article. Chlorophyll a is the principal constituent of PS I. Twenty per cent of isolated pigment-protein complexes contain one P700 per 20—30 chlorophyll a molecules the other 80% contain only chlorophyll a20). The physical and chemical properties of chlorophyll a and its role in photosynthesis have recently been described by Meeks77), Mauzerall75), Hoch60), Butler10), and other authors of the Encyclopedia of Plant Physiology NS Vol. 5. 

Relatively little is known about the physical and chemical properties of LCAT. This transesterifying enzyme has not yet been obtained in pure form even the most highly purified preparations of the enzyme are contaminated with other proteins. Consequently, a thorough assessment of the findings discussed above must wait until LCAT is sufficiently pure. 

Macromolecules are very much like the crystalline powder just described. A few polymers, usually biologically-active natural products like enzymes or proteins, have very specific structure, mass, repeat-unit sequence, and conformational architecture. These biopolymers are the exceptions in polymer chemistry, however. Most synthetic polymers or storage biopolymers are collections of molecules with different numbers of repeat units in the molecule. The individual molecules of a polymer sample thus differ in chain length, mass, and size. The molecular weight of a polymer sample is thus a distributed quantity. This variation in molecular weight amongst molecules in a sample has important implications, since, just as in the crystal dimension example, physical and chemical properties of the polymer sample depend on different measures of the molecular weight distribution. 

The consequences of such a conformational change could be dramatic for the physical and chemical properties of the protein and would explain the cytochrome c behavior. Related effects on electron transfer catalysis of the protein have been discussed elsewhere.40... 

Groves, M.J. and Teng, C.D. (1992). The effect of compaction and moisture on some physical and biological properties of proteins. In Stability of Protein Pharmaceuticals, Part A Chemical and Physical Pathways of Protein Degradation, T.J. Ahem and M.C. Manning, eds. Plenum Press, New York, 311-359. 

The most prominent feature of the chemistry of flavin is its redox properties. These properties make flavin especially suitable for its broad involvement in biological reactions. In the following the pH-dependent species formed in one- and two-electron reductions will be dealt with first, including their visible absorption and fluorescence properties. These physical properties form the basis of many kinetical and analytical studies. In Scheme 3 the structures refer to the free and protein-bound prosthetic groups (cf. Scheme 1). To study the physical properties of the flavocoenzymes often N(3)-alkylated lumiflavin (R = CH3) is used which is better soluble in a variety of solvents. Other physical and chemical properties of these species will be discussed subsequently. 

Bell, K. and McKenzie, H. A. 1976. The physical and chemical properties of whey proteins. In Milk Protein Workshop, Tanunda, South Australia. Northfield Research Laboratories, South Australian Department of Agriculture. 

The physical and chemical properties of the measurement site greatly influence accuracy of noninvasive clinical measurements. Noteworthy physical parameters include thickness, scattering properties, and temperature of the tissue at the measurement site. Chemical issues center on the molecular makeup of the tissue (water, protein, fats, amino acids, glycolytic structures, etc.) and the heterogeneous distribution of these chemical components throughout the measurement site. 

The proteome is the set of expressed proteins at a given time under defined conditions it is dynamic and varies according to the cell type and functional state. One of the main differences when working with proteins is that there is not an amplification methodology for proteins comparable to PCR. Physical and chemical diversity of proteins are also higher than nucleic acids. They differ among individuals, cell types, and within the same cell depending on cell activity and state. In addition, there are hundreds of different types of post-translational modifications (PTMs), which evidently will influence chemical properties and functions of proteins. PTMs are key to the control and... 

A number of useful computational tools have been developed for predicting the identity of unknown proteins based on the physical and chemical properties of amino acids and vice versa. Many of these tools are available through the Expert Protein Analysis System (ExPASy) at http //www.expasy.ch (Appel et al., 1994) and other servers. 

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