Heme structure of hemoglobin M Iwate [alpha 87(F8)His-->Tyr]: a UV and visible resonance Raman study.
Heme structures of a natural mutant hemoglobin (Hb), Hb M Iwate [alpha87(F8)His-->Tyr], and protonation of its F8-Tyr were examined with the 244-nm excited UV resonance Raman (UVRR) and the 406.7- and 441.6-nm excited visible resonance Raman (RR) spectroscopy. It was clarified from the UVRR bands at 1605 and 1166 cm(-)(1) characteristic of tyrosinate that the tyrosine (F8) of the abnormal subunit in Hb M Iwate adopts a deprotonated form. UV Raman bands of other Tyr residues indicated that the protein takes the T-quaternary structure even in the met form. Although both hemes of alpha and beta subunits in metHb A take a six-coordinate (6c) high-spin structure, the 406.7-nm excited RR spectrum of metHb M Iwate indicated that the abnormal alpha subunit adopts a 5c high-spin structure. The present results and our previous observation of the nu(Fe)(-)(O(tyrosine)) Raman band [Nagai et al. (1989) Biochemistry 28, 2418-2422] have proved that F8-tyrosinate is covalently bound to Fe(III) heme in the alpha subunit of Hb M Iwate. As a result, peripheral groups of porphyrin ring, especially the vinyl and the propionate side chains, were so strongly influenced that the RR spectrum in the low-frequency region excited at 406.7 nm is distinctly changed from the normal pattern. When Hb M Iwate was fully reduced, the characteristic UVRR bands of tyrosinate disappeared and the Raman bands of tyrosine at 1620 (Y8a), 1207 (Y7a), and 1177 cm(-)(1) (Y9a) increased in intensity. Coordination of distal His(E7) to the Fe(II) heme in the reduced alpha subunit of Hb M Iwate was proved by the observation of the nu(Fe)(-)(His) RR band in the 441.6-nm excited RR spectrum at the same frequency as that of its isolated alpha chain. The effects of the distal-His coordination on the heme appeared as a distortion of the peripheral groups of heme. A possible mechanism for the formation of a Fe(III)-tyrosinate bond in Hb M Iwate is discussed.
Nagai
M
M
School of Health Sciences, Kanazawa University Faculty of Medicine, Kodatsuno, Kanazawa 920-0942, Japan.
Aki
M
M
Li
R
R
Jin
Y
Y
Sakai
H
H
Nagatomo
S
S
Kitagawa
T
T
D019943:Amino Acid Substitution / Q000235:genetics; D004227:Dithionite; D006418:Heme / Q000737:chemistry*; D006441:Hemoglobin A / Q000737:chemistry; D006449:Hemoglobin M / Q000737:chemistry* / Q000235:genetics*; D006454:Hemoglobins / Q000737:chemistry; D006639:Histidine / Q000235:genetics*; D006801:Humans; D008706:Methemoglobin / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D019163:Reducing Agents; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods; D014443:Tyrosine / Q000235:genetics*
D006454:Hemoglobins; D010446:Peptide Fragments; D019163:Reducing Agents; D004227:Dithionite; D014443:Tyrosine; D006418:Heme; D006639:Histidine; C100003:deoxyhemoglobin; D008706:Methemoglobin; D006441:Hemoglobin A; C027542:hemoglobin M Iwate; D006449:Hemoglobin M