Studies on the Affinity of Heme to Proteins

Abstract

As is well known, when hemoglobin is denatured by addition of alkali and sodium dithionite, hemoglobin converts into “alkaline denatured globin hemochrome” in which the 5th and 6th coordination positions of the heme are saturated most probably with the imidazole groups of histidine. This alkaline denatured globin hemochrome is known to combine with as much as 24 hemes newly added, as previously reported by Holden (1) and Horiguchi (2). This fact seems to imply the participation of certain groups other than histidine in heme linkage. Further, it was also reported semiquantitatively (2) that the affinity of heme linked groups in hemoglobin seems to be much higher than that of free histidine. It is of great interest to explain the marked difference between their heme-combining affinities. Present authors intended to study more in detail the combining reaction of heme to free histidine, alkaline denatured proteins and proteinase digested hemoglobin.