Protein organic modifier

In addition to phenolic substances, there are other components present in foods which have no antioxidant activity of their own, but which increase that of phenolic antioxidants. They are called synergists, and they should be accounted for in any discussion of antioxidant activity. Polyvalent organic acids, amino acids, phospholipids (lecithin) and various chelating agents belong to this group. Proteins may modify the efficiency of antioxidants as they react with the reaction products of both antioxidants and synergists. 

Methanol, isopropanol, and 50 mM hexafluoroisopropanol were also evaluated for use as organic modifiers in the mobile phase. Little improvement to the solubility of whole proteins or their chromatographic separation was observed, however. 

In order to select a carrier solution composition which would provide an overall maximum response for MS detection, two modifiers were selected, acetonitrile and methanol, and two buffers, i.e. ammonium acetate (10 mmol pH 7.5) and ammonium formate (10 mmol L pH 7.5). Biotin and fluorescein-biotin were dissolved in various binding buffer-organic solvent mixtures ranging from 90 10 (v/v) to 50 50 (v/v) at two concentration levels (0.01 ng 1 ng pL ) and 20 pL were injected and analyzed by MS in full-scan and SIM mode. The maximum response was found with 50% methanol, which was about a factor 2x higher than for 10% methanol. Since the proteins can denaturate or protein-ligand complexes can dissociate at relatively low percentages of organic modifier in further experiments only 10% methanol is used in the carrier solution. 

Fractionation of proteins according to size utilizing cross-linked dextran or polyacrylamide gel columns was first demonstrated by Porath and Flodin 63 in 1959. This technique has become the most widely accepted method for separation and molecular weight determination of hydrophilic and some hydrophobic macromolecules using aqueous buffers with or without organic modifier. While this technique might not be unique in its ability to resolve and separate proteins, it is one additional simple and effective tool in the chemist s armamentarium. The theories behind size-exclusion HPLC and size-exclusion chromatography at low pressure are identical and are described in several publications. 31 34 36 39 44 64 65 ... 

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