Stability of the Cu(II) complexes of tripeptides, Cu(H-2L), in dynamic aspects;: L = tripeptides composed of various combinations of α-, β-, and γ-amino-acid residues.: Stopped-flow kinetic studies on the reaction of Cu(H-2L) with cysteine

rate constant (k(1+)) for the formation of ternary complexes, Cu(H-1L)(Cys(-)), from Cu(H-2L) and cysteine (Cys), where L denotes tripeptides composed of various combinations of alpha-, beta-, and gamma-amino-acid residues. The ligand-exchange reaction was examined by the stopped-flow spectrophotometric method. The Cu(H-2L) species, having 5-6-5- and 6-5-5-membered fused-chelate rings, were kinetically fairly stable; k(1+) = 2-3 x 10(4) M-1 s(-1). Other Cu(H-2L) species, having 5-5-5-, 5-5-6-, 5-5-7-, 5-6-6-, and 6-5-6-membered rings, reacted rapidly with Cys to form the Cu(H-1L)(Cys-) species; k(1+) greater than or equal to 1 x 10(5) M-1 s(-1). The Cu(H-1L)(Cys(-)) species, upon forming, successively reacted with Cys to afford a binary complex, Cu(Cys(-))(2). The Cu(H-1L)(Cys(-)) species, with the beta-Ala residue at the N-terminus, were kinetically labile to be rapidly transformed to Cu(Cys(-))(2).