Interaction between Serum Albumin and Mercaptoundecahydrododecaborate Ion (An Agent for Boron-Neutron Capture Therapy of Brain Tumor). I. Introductory Remarks and Preliminary Experiments

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The interaction between bovine serum albumin and dodecahydrododecaborate B₁₂H₁₂^2- or mercaptoundecahydrododecaborate B₁₂H₁₁SH^2- anion has been investigated by equilibrium dialysis, equilibrium distribution in and out of a Sephadex gel, gel-filtration-, ion-exchange-, and ion-retardation-chromatographies. The results have been discussed with the following conclusions. 1) Both borates are strongly bound to the albumin through ion-pair formation with cationic sites on the protein molecules. 2) This binding of ionic character can be readily broken up by ion-exchange or ion-retardation chromatography. 3) The latter borate shows, in addition, another mode of binding which is resistant against ion-exchange and ion-retardation resins. 4) This binding of covalent character is due to the formation of disulfide linkage between the boron cage of B₁₂H₁₁SH^2- and the albumin.