Polarographic catalytic hydrogen currents observed with native and modified bovine serum albumin

Catalytic hydrogen (presodium) currents (i_p.s.) obtained with bovine serum albumin (BSA), completely reduced BSA, ?(SH)₃₅, and ?(SCH₂COO)₃₅Na₃₅ have been studied in various buffers and at varying pH. At the same pH i_p.s.. of BSA increases with ammonium concentration in ammonia buffer and is considerably greater in ammonia than in borate and greater in the latter than in tris buffers. Calcium(chloride) greatly increases i_p.s. in all buffers, except in the presence of 8 M urea. Treatment of 1% BSA for 24 hours or longer with a large excess of formaldehyde in a phosphate buffer and dilution in a buffer reduces i_p.s. to very small values, but the calcium effect is now relatively much greater than before treatment. The same is true when the buffers after treatment are made 8 M in urea. Evidence is presented that the effect is due to a complexation of calcium with the reaction product of formaldehyde with amino and imino groups. With ?(SH)₃₅ practically no calcium effect on i_p.s. was observed. However, after reaction with formaldehyde in a borax buffer, i_p.s. is strongly reduced and after this treatment there is a large calcium effect. With ?(SCHC₂COO)₃₅Na₃₅i_p.s. is very poorly defined and occurs at more negative potential, and is much smaller than observed with BSA. There is again a distinct calcium effect. Presodium currents are also poorly defined with cystine and cysteine, a distinct calcium as well as formaldehyde effect being observed. Polarographic evidence is presented that sulfhydryl in cysteine reacts with formaldehyde. This accounts for the fact that after formaldehyde treatment i_p.s. with cystine is different from that with cysteine.