Abstract
Transglutaminase catalyzes the formation of ε-(γ-glutamyl)lysyl crosslinks and the sub-stitution of a variety of primary amines for the γ-carboxyamide groups of protein-bound glutaminyl residues. As a first step in the use of transglutaminase for enzymic modification of food proteins, the reactivity of bovine casein components (αs1-, β-, and K-caseins) in the transglutaminase reaction was compared, and the properties of casein modified by this enzyme were examined.
The reactivity of K-casein was lower than that of αs1-or β-caseins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that each casein component was poly-merized through formation of intermolecular crosslinks by transglutaminase.
Ultracentrifugal experiments in the absence of calcium ions revealed that complex for-mation between αs1-casein (or β-casein) and K-casein was not impaired by this modification. The functional properties of αs1- and β-caseins in the presence of calcium ions (e.g. precipi-tation and micelle formation) were essentially retained after the modification. These results suggest that transglutaminase would be a useful tool to polymerize casein without damaging its special properties.
