Interaction of triethyltin with cat hemoglobin: Identification of binding sites and effects on hemoglobin function

Binding of triethyltin to the cat hemoglobins (HbA and HbB) results in the “masking” of two of the freely reactive sulfhydryl groups (SH) within the hemoglobin tetramer. That the “masked” SH groups occur in position 13α of each α-subunit was demonstrated by the lack of labeling of cysteine 13α with [¹⁴C]N-ethylmaleimide when triethyltin is present. Studies with cat-human hybrid hemoglobins indicate that the α-subunit of the cat hemoglobins alone is involved in the formation of a complex with triethyltin. Using available data on the primary as well as three dimensional structures of animal hemoglobins, it is suggested the cysteine 13α and histidine 20α serve as axial ligands in the formation of a pentacoordinate triethyltin cat hemoglobin complex. The binding of triethyltin results in an increase in the oxygen affinity of the two cat hemoglobins.