Some observations on the reactive sulphydryl groups in haemoglobin

Abstract

A comparative study of the hemoglobins of several mammalian species has shown no correlation between the reactive, unreactive, or total SH group content and the weight of the animal. The number of reactive SH groups/molecule in the hemoglobins studied approximate either to 2 or to 4. The behavior of the reactive SH groups differs from that of cys-teine in 3 ways: (a) the rate of reaction of heavy-metal ions with the reactive SH groups is slower than with cysteine; (b) thiosulphate interferes with the reaction between Ag+ ions and the reactive SH groups of human hemoglobin, but not with cysteine; (c) the acid-base-titration curves of human hemoglobin in the presence and absence of phenyl-mercuric hydroxide suggest that the reactive SH groups are not ionized at pH values less than 10.