Formation of a ternary complex with serum albumin: an explanation for the effect of alpha-mercapto-beta-(2-furan) acrylic acid on rat plasma zinc clearance.

1. Four, six and eight hours after gavage of rats with alpha-mercapto-beta-(2-furan)acrylic acid (MFA) (25 mg/kg) serum zinc concentration was increased ten-fold over control levels and a mean molar ratio of 1 albumin:0-4 zinc:0-8 MFA was found for seventeen sera. 2. At pH 7-5 a maximum of 1 mole of MFA could be bound per mole of metal-free bovine serum albumin. 3. In the presence of zinc ion, albumin-zinc-MFA complexes formed, since for each mole of albumin-zinc complex an additional mole of MFA could be bound to albumin. Complexes up to a molar stoichiometry of 1 albumin:2 zinc:3 MFA were prepared. 4. MFA stabilized the albumin-zinc complex against dissociation. 5. Formation of similar complexes in vivo may account for the markedly delayed clearance of plasma zinc rats administered beta-aryl derivatives of alpha-mercapto-acrylic acid.