Isoelectric point proteins

The optimal buffer pH for a separation depends on the protein isoelectric point (pi) and the stability of the packing. In general, the use of a buffer at a... 

Albumin did not demonstrate any corrosive behavior to the copper and nickel films. The intensity of the 2100 cm 1 water association band, shown in Figure 4, did not change during the 4-hr period that albumin was initially exposed to the thin metal films. Even after 4 additional hours of exposure to the adsorbed protein film, the 2100 cm 1 band intensity remained unchanged, indicating that the copper and nickel films remained intact. Exposure of copper and nickel films to albumin above and below the protein isoelectric point did not alter these results. 

Protein Isoelectric Point (pi at 25°C) Relative Molecular Mass... 

At the second critical pH (pH,, ), which is usually below the protein isoelectric point, strong electrostatic interaction between positively charged protein molecules and anionic polysaccharide chains will cause soluble protein/polysaccharide complexes to aggregate into insoluble protein/polysaccharide complexes. For negatively charged weak acid-based (e.g., carboxylic acid) polysaccharides like pectin, with the decrease of pH below the pKa of the polysaccharide, protein (e.g., bovine serum albumin (BSA))/polysaccharide (e.g., pectin) insoluble complexes may dissociate into soluble complexes, or even non-interacted protein molecules and polysaccharide chains, due to the low charges of polysaccharide chains as well as the repulsion between the positively charged proteins (Dickinson 1998). 

Dawes, H., Boyes, S., Keene, J., Heatherbell, D. (1994). Protein instability of wines Influence of protein isoelectric point. Am. J. Enol. Vitic., 45, 319-326 Derckel, J.P., Legendre, L., Audran, J.C., Haye, B., Lambert, B. (1996). Chitinases of the grapevine (Vitis vinifera L.) five isoforms induced in leaves by salicylic acid are constitutively expressed in other tissues. Plant Sci., 119, 31-37... 

The very serious problem of fouling by proteins is corroborated by many publications [41,70,71]. Various parameters influencing the fouling behaviour have been studied. Clark et al. [70] discuss the influence of protein concentration, trans-membrane pressure, cross flow velocity and pH. For pore sizes of 0.1 pm (Membralox membranes), filtering bovine serum albumin, the flux has a minimum at the pH of the protein isoelectric point. Dumon and Barnier [71] show that the amount of protein adsorption depends on previous adsorption. Contacting with citrate or phosphate lowers a subsequent protein adsorption contacting with nitrate increases the protein adsorption. 

The 2D gel approach is ideal for identifying proteins with post-translational modifications, since small changes in protein isoelectric points and size result in dramatic changes in the position of the proteins in the gel. For example, proteins modified by phosphorylation move a considerable distance away from the parent, unmodified protein. Despite the improvements, 2D-PAGE remains technically complicated, and requires that at least triplicate samples be processed for statistical purposes. In addition, some classes of proteins are not detectable, including those that are rare (i.e. low abundance), small (i.e. under 2 kDa), glycosylated, or basic. 

The protein isoelectric point (pi) value is the pH at which the sum of acidic amino-add negative charges and of basic amino-add positive charges equals zero. It ranges between less than 3 and more than 12. 

SPI hardened with an aldehyde at or near the proteins isoelectric point ("pH 4.5 for soy protein) produces a material that is thermoplastic and absorbs <10% moisture during 24 h of soaking. An aqueous suspension of the formaldehyde-hardened SPI can be used as a laminating material for Kraft paper. Laminating material made from soy plastics has similar properties to the more expensive phenol and urea laminating materials, but is less water-resistant. SPI was discontinued during the early 1950s in favor of modified soybean meals used as modifiers and extenders in PF plastics. 

The literature contains accounts of two highly basic proteins (isoelectric points 8.8 and 9.4), a powerful hemagglutinating protein, and lactoferrin in boar seminal vesicle (210-213), and of various bulk proteins (including fractions that resemble calmodulin in binding calcium tenaciously) in bull seminal plasma (214). Proteins of seminal plasmas of other mammalian species that probably originate from vesicular secretions are reviewed by Mann (4) and Mann and Lutwak-Mann (5). 

Antidiabetic present in the pancreas (Islets of Langerhems). Cryst. M.p. 233° after turning brown at 215°. Laevorotatory. Chemical properties are those of a typical protein. Isoelectric point, Pb 5 3-5-35. 

It has been reported [57, 58] that the formation of soluble PE-P complexes is initiated at a specific pH called the critical pH (pHc), which is a function of ionic strength, the protein isoelectric point, and the PE density charge [59]. For polycations, pHc preceded the pH of visual phase separation, named pH( ). This parameter is defined as the pH at which the half maximal value of turbidity is achieved. Since these non-soluble complexes can be considered a phase separation, the ionic strength dependences of both pHc and pH([), can be viewed as phase boundaries. The phenomenon has been ascribed to the attraction between PE charges and oppositely charged patches on the protein surface [5]. This could be applied to complexation between oppositely charged proteins and PE. 

Extract with water at protein isoelectric point Water-soluble ... 

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