| Research Abstract |
In the hemoglobin (Hb) molecule, the proximal and distal histidines are the most important for preventing the ferrous heme from oxidation and for the cooperative ligand binding. Hbs M are mutant hemoglobins, one of these histidines of which is replaced with tyrosine, and their hemes are stabilized usually in ferric state. Although patients of Hbs M show obvious cyanosis, only individuals with Hb M Saskatoon (beta E7 His-Tyr) have less cyanosis than those of the other Hbs M (Hb M Iwate, alpha F8 His-Tyr; Hb M Boston, alpha E7 His-Tyr; Hb M Hyde Park, beta F8 His-Tyr). In order to know why such symptoms for indivisuals with Hb M differ from each other, we have investigated the reducibility of abnormal chains of Hbs M by erythrocyte methemoglobin reductases and the structure of abnormal chains by using resonance Raman (RR), and electron spin resonance (ESR) spectrometry.
Under anaerobic conditions, abnormal chains of Hb M Saskatoon was reduced by methemoglobin reductases purified from huma
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n erythrocytes at almost the same rate as was metHb A. However, abnormal chains of the other Hbs M were scarcely reduced by these enzymes. In fact, we have found recently that more than half of the abnormal chains remained in ferrous state in the fresh bloods of individuals with Hb M Sastakoon.
In the RR spectra, all of four Hbs M exhibited the fingerprint bands for the Fe-tyrosinate proteins (1600, 1500 and 1270 cm^<-1>) and Fe-tyrosinate proteins (1600, 1500 and 1270 cm^<-1>) and Fe-tyrosinate stretching frequency in abnormal chain of Hb M Saskatoon was the lowest among them. However, only Hb M Saskatoon displayed the Raman spectral pattern of a six-coordinate heme for the abnormal subunit while others displayed that of a five-cooordinate heme. From these observations, it is concluded that the heme in abnormal chains of Hb M Iwate, Hb M Boston and Hb M Hyde Park, bind only with the substituted tyrosine, whereas that of Hb M Saskatoon binds weakly both the proximal histidine and the substituted tyrosine.
As abnormal chains of Hbs M can bind with carbonmonooxide (CO) after reduction by dithionite, we examined their unusual lignad binding properties by RR, infrared, and ^<13>C-NMR spectroscopy and discussed the role of the proximal and distal His on ligand binding properties in normal hemoglobin. Less
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