Sulphydryl groups in haemoglobins

Abstract

Numbers of available sulfydryl groups in the native and sodium dodecylsulfate denatured hemoglobins of horse, ox, man and sheep were determined by amperometric titration with AgNO3 and HgCl2. Native horse, ox and human hemoglobins have 4 sulfydryl groups as 2 pairs of closely neighboring groups. Native sheep hemoglobin shows 8 sulfydryl groups as 4 such pairs. Horse hemoglobin denatured with sodium dodecylsulfate has altogether 6 sulfydryl groups probably situated symmetrically with respect to a diad axis as 2 clusters of 3. Since the number of cysteine-cystine sulfur atoms is 6, there can be no disulfide linkages in this hemoglobin. Denaturation of human hemoglobin with sodium dodecylsulfate reveals the presence of 8 sulfydryl groups, 6 of which are probably arranged in 2 clusters of 3 as in horse hemoglobin, while the remaining 2 appear to be separate.