The differential effects of carbon monoxide and oxygen on the pressure dissociation of Lumbricus terrestris hemoglobin.
We have explored the subunit affinities of Lumbricus terrestris hemoglobin (LtHb) under a variety of conditions using high-pressure spectroscopy. While only small changes were observed for LtHb-oxy below 1.0 kbar, higher pressures resulted in a 1000 cm-1 red shift and 2-fold increase in fluorescence intensity with a concomitant 12-fold decrease in scattering intensity, all of which reached completion by approx. 2.2 kbar. In the presence of 1 M MgCl2 or at acidic pH (4.2), the curves shifted by 400 and 1000 bar corresponding to significant destabilization. At pH 9.1, the initial spectral parameters were almost equal to the final endpoints and were unaffected by pressure. While the pressure curve of the CO form was similar to the oxy form at pH 7.2, the midpoints of the other samples were shifted to higher pressures relative to their oxy counterpart, indicating tighter subunit contacts. This stabilization was unexpected based upon the sequence homology to vertebrate hemoglobins, and the minimal structural differences between these two liganded forms of human hemoglobin. These data indicate that the differences are the result of the additive nature of the interactions involved in subunit packing whose effects become significant in larger aggregates.
Hirsch
R E
RE
Department of Medicine, Albert Einstein College of Medicine, Bronx, NY.
Harrington
J P
JP
Scarlata
S F
SF
D000818:Animals; D002248:Carbon Monoxide / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry*; D006874:Hydrostatic Pressure; D009835:Oligochaeta; D010100:Oxygen / Q000737:chemistry*; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence
D006454:Hemoglobins; D002248:Carbon Monoxide; D010100:Oxygen