Influence of Blood Proteins on Biomedical Analysis. VI. Effect of Bovine Serum Albumin on the Color Reaction of Xanthurenic Acid with 4-Aminoantipyrine-Inhibition of Antipyrine Red Production by Bovine Serum Albumin

In order to characterize the amplifying effect of bovine serum albumin (BSA) on the coloration of xanthurenic acid (XA) with 4-aminoantipyrine (4-AAP) and an oxidizing agent (potassium ferricyanide), the effects of amount of BSA, time of BSA addition to the reaction mixture, and the side reaction producing antipyrine red were studied. The BSA-induced recovery of the coloration was 100% when BSA was added to the reaction mixture within 3 min after the initiation of the color reaction, though after 5 min it was not more than 50%. A lower temperature, a lower concentration of potassium ferricyanide and a higher concentration of 4-AAP in the reaction mixture before the BSA addition enhanced the BSA-induced recovery effect on the coloration. The production of antipyrine red was inhibited by BSA in the reaction mixture without XA. In conclusion, the present results suggest that the BSA-induced amplifying effect on the color reaction of XA with 4-AAP and potassium ferricyanide is based on the inhibition of the side reaction which produces antipyrine red by the bimolecular condensation of 4-AAP.