The binding of cupric ions to 1-carboxymethylhistidine-119-ribonuclease.

Binding of Cu(2+) by 1-carboxymethylhistidine-119-ribonuclease was investigated by using diligand metal ion buffers. A single Cu(2+)-binding site was found over the Cu(2+) concentration range studied. The binding constants for this site were 8.33x10(5) (+/-2%)m(-1) and 1.57x10(4) (+/-6%)m(-1) at pH7.0 and 6.1 respectively. An estimate of the pH-independent Cu(2+)-binding constant suggests that the most avid Cu(2+)-binding site has disappeared after carboxymethylation. This is consistent with an earlier report that binding of Cu(2+) at the most avid site is associated with the loss of enzymic activity.