Abstract
1. Dissociation of histidine hemichrome coincided well with a theoretical second order dissociation curve. The change of pK in function of pH was elucidated by taking into consideration the dissociations of imidazole-NH of histidine and of hematin iron. The following theoretical equation was found to account for the results obtained.
pK=pKo-2log(1+[H+]/Ka)-log (1+Kb/[H+])
pK0 was found to be 3.6 on an average, at room temperature of 20°. 2. Alkaline denatured proteins combined with much more heme molecules than expected from their histidine contents. The number of heme linked groups was estimated as 68, 26, 40 and 32 in horse hemoglobin, bovine serum albumin, horse serum albumin and human serum γ-globulin, respectively. The heme linked groups of alkaline denatured proteins were deduced to be not carboxyl groups of acidic amino acids but nitrogenous groups of basic amino acids.
3. The affinity of alkaline denatured protein towards heme was decreased remarkably by proteinase digestion.
The authors wish to express their gratitude to Miss M. Shinoda for her technical assistance, to Dr. H. Hirai for the gift of horse serum albumin and human serum γ-globulin, and to Dr. T. Kusunoki for the sample of bovine serum albumin. Thanks are also due to the Scientific Research Fund of the Ministry of Education for grant. The essential part of this study was published in Japanese elsewhere (15, 16).
