Abstract
The potential of using chemical modification as a tool to determine structure-function relationships was examined using one standard protein namely bovine serum albumin. The chemical modifications investigated included succinylation with succinic anhydride; thiolation, using N-acetyl homocysteine thiolactone; guanidination with O-methylisourea; the addition of cysteine hydrochloride; attachment of valine using an N-carboxyl anhydride derivative and of butylamine, putrescine and lysine via carbodiimide mediated condensation reactions. The native and modified proteins were subjected to a set of standard tests including assessment of amino, sulphydryl and hydrophobic groups and changes in the pH titration curve, amino acid composition, electrophoretic patterns and circular dichroism spectra. The functional properties examined included gelling, whipping and emulsification. The blocking of amino groups by succinylation and thiolation resulted in reduced functional properties whereas the addition of the hydrophobic amino acid valine resulted in improved functional properties. Improved whipping resulted when succinylated BSA was inadequately purified and in the presence of calcium the gelling strength of succinylated protein was significantly increased compared to the native BSA. In addition, ultrafiltration decreased the gelling properties of BSA. Cysteine modified samples showed little change in physicochemical or functional properties. A limited modification by guanidination or by carbodiimide condensation showed improved functional properties whereas an extensive modification resulted in poor functional properties. This was thought to be due to detrimental conformational changes in the extensively modified samples. A positive interaction between modified samples was shown to be dependent on the availability of amino groups and not the difference in charge as was expected. All modified samples showed little improvement in emulsification properties. In conclusion, the analysis of chemical modifications in the evaluation of certain structure-function relationships proved useful, but in order to elucidate the precise mechanisms involved, the information obtained from other methods of evaluation will be required.