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A chromatographic method for estimating hydrophobic and electrostatic surface properties of soluble proteins Wijewickreme, Arosha Nilmini


In this research experiments were carried out to estimate hydrophobic and electrostatic interactions in soluble proteins. Five proteins, lysozyme, lactalbumin, ovalbumin, myoglobin and ribonuclease-A were chromatographed isocratically on a HIC column at several molalities (0.3-1.3m) of each of three different neutral salts, ferrous sulfate, ammonium sulfate and sodium sulfate. The calculated retention coefficients were then fitted to a recently developed chromatographic model in two ways. a) Multiple regression analysis was conducted to estimate C values according to the non-linear model (log k = A + B log m + C m) . b) Simple regression analysis was conducted to estimate C′ values according to the linear model (log k = A′ + C′m) at higher salt concentrations (above 0.3m). Results indicated that C′ values better estimate the hydrophobic interactions than C values, in experiments conducted only at higher salt concentrations. The comparison of C and C′ values with ANS, CPA, and Bigelow's average hydrophobicity indices showed no clear correlations. But, omission of ovalbumin improved the correlation coefficient of C′ with ANS. Both parameters indicated straight line relationships with molal surface tension increment of salts. Further, the same model was used to estimate the hydrophobic and electrostatic interactions in protein-protein interactions. Lysozyme and avidin were chromatographed on a lysozyme immobilized affinity column. Lysozyme-lysozyme interaction showed more affinity for hydrophobic interactions at low pH values. Avidin-lysozyme interaction showed both hydrophophobic and electrostatic interactions. Both interactions showed a greater change in the strength of hydrophobic interaction rather than the surface area of interaction, to changing pH.

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