Proteins surface active property

Protein-water interaction plays an important role in the determination and maintenance of the three-dimensional structure of proteins. Water modified the physicochemical properties of proteins. Therefore, protein-water interactions have been the subject of intensive study and have provided significant advances in our understanding of the involvement of water in protein functionality, stability, and dynamics [6]. The thermodynamics of protein-water interaction directly affects dispersibility, wettability, swelling, and solubility of proteins. Surface-active properties of proteins are simply the result of the thermodynamically unfavorable interaction of exposed nonpolar patches of proteins with solvent water. 

Comparative study of LB films of cytochrome P450 wild type and recombinant revealed similar surface-active properties of the samples. CD spectra have shown that the secondary structure of these proteins is practically identical. Improved thermal stability is also similar for LB films built up from these proteins. Marked differences for LB films of wild type and recombinant protein were observed in surface density and the thickness of the deposited layer. These differences can be explained by improved purity of the recombinant sample. In fact, impurity can disturb layer formation, preventing closest packing and diminishing the surface density and the average monolayer thickness. Decreased purity of... 

Stratum corneum, the nonliving layer of skin, is refractory as a substrate for chemical reactions, hut it has a strong physical affinity for water. The chemical stability of stratum corneum is evident in its mechanical barriers which include insoluble cell membranes, matrix-embedded fibers, specialized junctions between cells, and intercellular cement. The hygroscopic properties of stratum corneum appear to reside in an 80 A-thick mixture of surface-active proteins and lipids that forms concentric hydrophilic interfaces about each fiber. This combination of structural features and surface-active properties can explain how stratum corneum retains body fluids and prevents disruption of living cells by environmental water or chemicals. 

Many contaminants in wastewater today, such as dissolved dyestuffs, lignins, detergents, proteins, fatty acids, tannins, and so on, possess surface-active properties that decrease surface tension and oxygen transfer rate, but increase the demand for dissolved oxygen. Particularly, the sharp reduction in surface tension of water by these pollutants seems to be a basic cause of increasing the susceptibility of aquatic life to the surfactant poison. 

Pulmonary surfactant is a complex of lipids and proteins with unique surface active properties that is synthesized exclusively in alveolar type II cells. The composition of surfactant is 90% lipids and 5-10% surfactant-specific proteins. The lipid component is made up of dipalmitoylphosphatidylcholine (also called lecithin, 70-80%) and another major phospholipid, phosphatidyl-glycerol (PG, 10%). The remainder of the phospholipids of surfactant are phosphatidylinositol (PI), phos-phatidylethanolamine (PE), and phosphatidylserine (PS). Immature surfactant contains higher amounts of PI compared to PG. Thus, a low ratio of PG to PI indicates lung immaturity. Cholesterol, a neutral lipid, is also a constituent of the lipid component of surfactant. 

The surface active properties of proteins are related to their ability to lower the interfacial tension between air/water or oil/water interfaces. Surface activity is a function of the ease with which proteins can diffuse to, adsorb at, unfold, and rearrange at an interface (11,12). Thus, size, native structure and solubility in the aqueous phase are closely correlated with the surface activity of proteins in model systems (13-16). 

In order to elucidate relationships between surface active and film forming properties of food proteins, it is useful to examine the surface active properties of proteins whose physical and molecular properties are well characterized e.g. -casein, bovine serum albumin (BSA), lysozyme ( ), and -lactoglobulin (b-Lg) (2jL). These represent a range of tertiary structures for soluble proteins. Lysozyme is a rigid and roughly ellipsoidal molecule, whereas the hydrophobic -casein molecule is mostly a random coil structure. The b-Lg molecule consists almost entirely of antiparallel -sheet strands organized into a flattened cone ( ). 

Sucrose esters of fatty acids having 12 or more carbon atoms display surface active properties. Most of them are odourless and tasteless (or slightly bitter) allowing them to find applications both in food and personal care products [17]. Sucroesters were approved and freely permitted in Japan for use as food additives in 1959 for both their emulsifying ability and their heat stability. In addition, they are well known to protect food proteins from thermal denaturation and inhibit the growth of Escherichia coli and other bacteria. 

AES Toxicity. The effect of surfactant structure on toxicity has obvious importance. With AES, there is the tendency of decreased toxicity with increasing EO numbers, at least when comparing AES with the same hydrophobe. Also, increasing alkyl chain length in the hydrophobe will generally increase toxicity. These trends are understandable when one considers that the toxicity mechanism of surfactants, namely membrane disruption and protein denaturation, is a function of the surface-active properties of surfactants. Therefore, the alteration of surface-active properties via structure changes should affect toxicity. 

Proteins are by nature amphipathic or amphiphilic molecules that is, they contain both a hydrophobic (nonpolar) and a hydrophilic (polar) moiety. However, natural proteins per se are not used as commercial surfactants. Rather, proteins are modified by chemical or enzymatic means to products with surface-active properties. The use of modified proteins based on casein, soybean, albumen, collagen, or keratin is not new [5]. The Maywood Chemical Company introduced commercial protein-based surfactants (PBS) in the United States in 1937. They were primarily condensation products of fatty acids with hydrolyzed proteins [5], Renewed interest in PBS has occurred not only as products based on renewable raw materials (i.e., proteins and fatty acids), but also as a solution to waste disposal for animal and vegetable protein byproducts [5], Among the commercial PBS, the following trade names have been active Crotein, Lexein, Magpon Polypeptide, Protolate, Sol-U-Teins, and Super Pro. 

Polymers with which we will deal throughout this chapter are water soluble. They can be either ionic or nonionic. Some of them are synthetic, others are of biological origin (proteins, for instance). Both homopolymers and heteropolymers exist. Some polymers own amphiphilic monomers that induce surface-active properties to the whole polymeric structure. Water plays a very important role in determining the polymer properties in solution. The properties are also greatly modified by the addition of salts or by a pH modification. Frequently encountered nonionic polymers in polymer-surfactant interactions and their subsequent adsorption behavior at solid surfaces are poly(ethylene oxide) (PEO), poly(vinyl pyrrolidone) (PVP), polyacrylamide, and poly(vinyl alcohol). 

Yu SH, Possmayer F. Role of bovine pulmonary surfaetant-associated proteins in the surface active property of phospholipid mixtures. Bioehim Biophys Acta 1990 1046 233-241. 

Animal experimental models of nickel-induced skin sensitivity are few and have been conducted only under very specialized conditions (USEPA 1986). Studies examining the mechanism of nickel contact sensitization and its extent in wildlife are needed (USPHS 1993). The importance of the surface properties and crystalline structure of nickel compounds in relation to their reactivity and protein-binding activities is well documented. It is therefore necessary to identify clearly the nickel compounds to which exposure occurs (Sunderman etal. 1984). Acute and chronic dermal and... 

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