Brdicka currents observed with bovine serum albumin and completely reduced bovine serum albumin in the presence of urea.

In ammonia buffers of varying composition and pH, native bovine serum albumin and completely reduced bovine serum albumin, denoted by p(SH)35, yield quite different Brdicka current-voltage (i-E) curves, but they are identical in the presence of 5 mM calcium chloride. This means that in the presence of calcium, bovine serum albumin becomes completely reduced to p(SH)35. In 8 M urea and ammonia buffers the Brdicka i-E patterns of serum albumin and p(SH)35 are identical even in the absence of calcium, the effect of calcium on the first wave being negligible while calcium slightly increases the second wave. The maximum polarographic effect is attained at urea concentrations of about 5-6 M. Quite generally, the appearance of a second Brdicka wave is attributed to complexation of Co(II) with S- and a group of ligands that is different on the second than on the first wave. The effect of calcium on Brdicka currents of bovine serum albumin in the absence of urea is attributed to an orientation of the protein on the surface of the electrode such that all disulfide groups are reduced and with other ligands can complex with Co(ii). Denaturation of bovine serum albumin in buffers with a pH less than 10.5, and which are 8 M in area, is (polarographically) completely reversible if dilution is made within 15 minutes after preparation. Changes in Brdlcka I-E patterns upon longer aging at varying pH are attributed-in part at least-to dimerization of the denatured protein by interaction of pS- in one molecule with -S-S-in another.