A model protein, ribonuclease A (bovine pancreas), was examined for it
s ability to coordinate Ni2+ and promote selective oxidation. In the p
resence of a peracid such as monopersulfate, HSO5-, nickel induced the
monomeric RNase A to form dimers, trimers, tetramers, and higher olig
omers without producing fragmentation of the polypeptide backbone. Co2
+ and to a lesser extent Cu2+ exhibited similar activity. The nickel-d
ependent reaction appeared to result from a specific association betwe
en the protein and Ni2+ that allowed for transient and in situ oxidati
on of the bound nickel to yield intermolecular tyrosine-tyrosine cross
-links. Macrocylic nickel complexes that had previously been shown to
promote guanine oxidation were unable to mimic the activity of the fre
e metal salt. Amino acid analysis of the protein dimer confirmed the e
xpected consumption of one tyrosine per polypeptide and formation of d
ityrosine. The presence of excess tyrosine efficiently inhibited forma
tion of the protein dimer and produced instead a ribonuclease-tyrosine
cross-link. In contrast, high concentrations of the hydroxyl radical
quenching agent mannitol only partially inhibited ribonuclease dimeriz
ation. The polypeptide-mediated activation of nickel and its subsequen
t reactivity mimic a process that could contribute to the adverse effe
cts of nickel in vivo.