Effect of antibody on interaction between vitamin B2 and riboflavin apoprotein

1. Dissociation of riboflavin from flavoprotein and from the flavoprotein-antibody complex occurs under the same conditions. 2. The precipitated apoprotein-antibody complex retains 15% of the apoprotein capacity to bind riboflavin. After solubilization of the complex in 0.3 M-KCl or 1 M-urea, the binding of riboflavin amounts to 80 - 90% of its capacity. 3. The apoprotein modified by oxidation of 50% of tryptophan residues loses the ability to bind riboflavin but its immunological reactivity with the anti-flavoprotein antibody is similar to that of native apoprotein. The apoprotein with all tryptophan residues oxidized shows much lower immunoreactivity. 4. The obtained results suggest that in riboflavin flavoprotein the region around the riboflavin-binding site does not show the properties of an antigenic determinant.