Hyperfine-shifted proton resonances exchangeable, deoxy

Fig. 45. 250-MHz H NMR spectra of exchangeable proton resonances and deoxy hyperfine-shifted proton resonances of 15% Hb M Milwaukee (p67Val — Glu, a2p2 ) as a function of the concentration of inositol hexaphosphate in 0.1 M Bis-Tris in H20 at pH 6.6 and 30°C. The spectrum of Hb A is included for comparison. [Adapted from Fung et al. (1977)].

Fig. 49. 600-MHz H NMR spectra of cross-linked mixed-valency asymmetric hybrid hemoglobin (a+CNp)A(aP)cXL, in deoxy and CO forms, in the presence of 0.1 Af phosphate at pH 6.8 and 21°C. (A) Hyperfine-shifted proton resonances in D20 (B) exchangeable and hyperfine-shifted proton resonances in H20. [From Miura and Ho (1982)].

C. Deoxy-Hb A Hyperfine-Shifted, Exchangeable Proton Resonances, NgH, of Proximal Histidyl Residues... 

F. a. Deoxy-Hb A Hyperfine-Shifted and Exchangeable Proton Resonances in H20... 

Proximal Histidyl NzH Resonances. In the H NMR spectrum of deoxy-Hb A in H2O two low-field resonances occur at + 58.5 and +71.6 ppm downfield from H20 (La Mar et al., 1977 Takahashi et al., 1980). These two resonances disappear in the presence of D20 and have been assigned to the hyperfine-shifted NsH-exchangeable protons of the proximal histidyl residues (F8) of the a and p chains of deoxy-Hb A (Takahashi et al., 1980 La Mar et al., 1980). In Fig. 17, it is clear that the resonance at + 71 ppm is missing in Hb M Milwaukee, suggesting that this resonance comes from the p chain and the resonance at +58.5 ppm from the a chain. Hb M Boston has only the resonance at +71 ppm, which confirms the assignment of the +71-ppm resonance to the N8H proton of the proximal histidine of the P chain and the + 58.5-ppm resonance to the corresponding residue in the a chain (Takahashi et al., 1980). The fact that the a- and P-heme resonances are clearly separated indicates that the conformations of the proximal histidyl residues are different in the a and P chains of deoxy-Hb A. 

Fig. 28. 300-MHz hyperfine-shifted exchangeable proton resonances of proximal histidyl residues of the a and 0 chains of deoxy-Hb A. (A) 3.0 mM Hb A in 0.1 M Bis—Tris (95% deoxy-Hb A) (B) freshly lysed red blood cells, 4.7 mM Hb A (90% deoxy-Hb A) (C) freshly packed red blood cells (75% deoxy-Hb A). The broad dips in spectra B and C are due to membranes and other cell components. [From Yao et al. (1986)].

Fig. 56. H NMR spectra of deoxy-des-Arg(al41)-Hb A and deoxy[a(des-Arg)3]A[ 3]cXL in 0.1 M Bis—Tris, 0.1 At Tris, and 0.2 M chloride in 95% H20 and 5% D20. (A) 300-MHz H NMR spectra of hyperfine-shifted exchangeable N H of proximal histidyl residues (B) 600-MHz H NMR spectra of exchangeable proton resonances. [From Miura and Ho (1984)].

As also shown in Fig 57A, for deoxy[a(des-Arg-Tyr)(3]A[a 3]cXL at pH 6.0, about half the intensity of the hyperfine-shifted proximal histidyl N8H exchangeable proton resonances has already shifted downfield by about 15 ppm, but the remaining resonance remains at a position close to that of the a-subunit proximal histidyl N8H proton resonance in intact Hb A. It is reasonable to assign the resonance that remains unchanged to the normal intact a subunit of [a(3]c in deoxy[a(des-Arg-Tyr)(5]A[a(5]cXL. In correspondence with the shifted N8H proton resonance of a(des-Arg-Tyr), both resonances at +9.2 and +6.3 ppm from H20 have lost about half of their respective intensities, and they disappear when the pH is raised to 8.6. The increase in pH also causes the a-subunit histidyl N8H exchangeable proton resonance, normally occurring around +57... 

Figure 59 shows the H NMR spectra of deoxy[a(des-Arg)P]A-[a0(NES)]cXL and deoxy[a(des-Arg)P(NES)]A[aP]cXL. At low pH, both modified Hbs have hyperfine-shifted proximal histidyl N8H exchangeable proton resonances around + 60 ppm from H20, presumably due to the unmodified a subunits, but have reduced intensity... 

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