Charged proteins

Caramel color can be made with either positively or negatively charged particles. This allows manufacturers to use negative colloidal caramel in acidic soft drinks, and positive colloidal caramel in beers and soy sauces. Beer has positively charged proteins suspended in it, and soy sauce has a high salt content that requires the more salt-tolerant positive caramel color. 

Irish moss extract, or carrageenin, is a negatively charged polymer which reacts with positively charged protein molecules, imparting rapid increase in mix viscosity. There are many types used for ice cream, depending on the final use. It is generally used in conjunction with CMC or locust bean to prevent mix separation. Levels between 0.02 and 0.10% are recommended. 

Lee K, Fitch CA, Lecomte JT, Garcfa-Moreno EB (2002) Electrostatic effects in highly charged proteins Salt sensitivity of pKa values of histidines in staphylococcal nuclease. Biochemistry 41 5656-5667. 

Multiply charged proteins can also be partially sequenced, and microsequences of proteins isolated from several microorganisms have been reported, accomplished with electrospray ionization and FTMS.23,90 Nonadjacent fragment ions may be used to identify bacterial proteins in these top-down strategies.91 In all cases these sequences could be related by bioinformatics to the parent species. An obvious extension would be to characterize proteins from intact microorganisms in this way. In at least one instance a microsequence has been obtained from a protein released from a contaminated intact bacteriophage sample (MS2) to provide a chemotaxonomic identification.77 This work was carried out in an ion trap mass spectrometer. 

Figure 6.11 Principle of ion-exchange chromatography, in this case anion exchange chromatography. The chromatographic beads exhibit an overall positive charge. Proteins displaying a nett negative charge at the pH selected for the chromatography will bind to the beads due to electrostatic interactions...

P2 protein. PNS myelin contains a positively charged protein different from MBP that is referred to as P2 (Mr — 15,000). It is unrelated in sequence to MBP and is a member of a family of cytoplasmic fatty acid binding proteins (FABP) that are present in a variety of cell types [25]. The amount of P2 protein is variable among species, accounting for about 15% of total protein in bovine PNS myelin, 5% in humans and less than 1% in rodents. P2 protein is generally considered a PNS myelin protein but it is expressed in small amounts in CNS myelin sheaths of some species. P2 is an antigen for experimental allergic neuritis, the PNS counterpart of EAE (see Chs 36 and 38). P2 appears to be present in the major dense line of myelin sheaths, where it may play a structural role similar to MBP... 

Direct staining of proteins (e. g., after electrophoretic separation in polyacrylamide gels) can be achieved by treatment with dyes like Coomassie Brilliant Blue R-250 [146] (Fig. 7), which binds positively charged proteins in an acidic fixation buffer, allowing detection down to 0.1 pg of protein. 

Similar well-shaped responses have been obtained at a gold electrode using the aminoglycoside neomycin (neomycin sulfate), which is a positively charged promoter favouring the electrostatic interaction with negatively charged proteins.36... 

Fig. 11.20. Theoretical peak shape for a hypothetical singly charged protein ion of Mr = 15,300 at different settings of resolution. Reproduced from Ref. [98] by permission. John Wiley Sons, 1992.

The tissue cells exist in an electrically charged environment. To prevent antibodies from binding because of excess charges on the tissue surface, a proteinaceous solution is used to bind to these sites in advance of the antibody incubations. A 10% normal animal serum in PBS is used, obtained from the same species as that providing the secondary or detecting system antibody. The charged protein mol-... 

Incubate in the 10% animal serum in PBS overnight at 4°C. The charged protein molecules of the serum will bind to available sites, preventing the antibody reagents from binding to these areas nonspecifically (see Note 1). 

Additives such as polyethylene glycol, cationic antibiotics, polymers, small uncharged molecules, and negatively charged proteins have been used extensively in order to avoid the denaturing of enzymes or to improve the sensitivity and operational stability of biosensors. DNA has been proposed as an additive to improve the response and stability of biosensors based on CP. The biomolecules studied, such as tyrosinase [93], peroxidase [94], cytochrome C [95], have been shown to improve its performance by using adsorbed DNA within CP as an additive. 

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