The Reactions of the Sulfhydryl Groups of Human Hemoglobin &*

The rates at which the sulfhydryl groups on each chain of hemoglobin fi4 react with N-ethylmaleimide and iodoacetate have been measured. The sulfhydryl group at position 93 reacts with both alkylating agents at approximately the same rate as normal liganded hemoglobin. The sulfhydryl group at position 112, which is not available in normal hemoglobin, reacts in hemoglobin f14 and does so much more rapidly than does the sulfhydryl at position 93. The rapidly and slowly reacting groups were identified by isolation of tryptic peptides labeled with 14C-N-ethyhnaleimide or 14C-iodoacetate. Because of the different rates of reaction of the two sulfhydryl groups, it was possible to produce a derivative carboxymethylated only at position 112. This modification makes the ,8 chains unable to form tetramers. They have a sedimentation coefficient of 1.88 S which corresponds to monomers.