NUCLEAR MAGNETIC RESONANCE STUDIES OF HEMOGLOBINS, III. EVIDENCE FOR THE NONEQUIVALENCE OF α- AND β-CHAINS IN AZIDE DERIVATIVES OF METHEMOGLOBINS

Abstract

Nuclear magnetic resonance spectroscopy (100-MHz proton) was used to study the low-spin (S = 1/2) azide derivatives of human adult (alpha(2)beta(2)), human fetal (alpha(2)gamma(2)), Zürich (alpha(2)beta(2) (63 His --> Arg)), and horse (alpha(2)'beta(2)') methemoglobins, as well as whale metmyoglobin in 0.1 M deuterated phosphate at pD 7 and at 31 degrees C. The experimental results indicate that the azide-bound heme groups of the alpha- and beta-chains in human adult methemoglobin and of the alpha- and gamma-chains in fetal methemoglobin are not equivalent. The affinity of the beta- or gamma-chain for azide ion appears larger than that of the alpha-chain. The nuclar magnetic resonance spectrum of hemoglobin Zürich shows that the environment of the azide-heme complex in the abnormal beta-chain is altered by the substitution of arginine for histidine in the beta-63 position, while the alpha-heme environment remains unaffected.