Structural model for the trialkyltin binding site on cat hemoglobin.

The binding site for trialkyltin complexes on the alpha- chain of cat oxyhemoglobins is proposed to involve the SG and NE2 atoms of Cys-13 and His-113 respectively. On deoxygenation, the conformation of this region changes substantially, allowing complexation only through the ND1 nitrogen atom of His-113, a much less favorable interaction. Thus the model presented explains the preferential binding of trialkyltin complexes to R-state cat hemoglobin and suggests the type of interaction that is likely to occur between these compounds and a variety of less well-characterized enzymes to produce the metabolic effects that trialkyltin complexes are known to produce in vivo.