Interaction of XXXX with intact oxyhemoglobin.

@entity1 @entity1450 @entity10108 @entity26 @entity16920 @entity7887 @entity7888 @entity1391 @entity13880 @entity29404 @entity1446
In @entity7887 and @entity10108 , free @entity7888 ( @entity13880 ) and @entity1450 ( @entity29404 ), respectively, accumulate in erythrocytes. That PPIX and @entity29404 bind to @entity1 hemoglobin A ( @entity16920 ) is established, but the site of binding is still a matter of controversy. We investigated the interaction of @entity29404 with intact, tetrameric oxy @entity16920 , using batch microcalorimetry, front-face fluorometry, absorption difference spectroscopy, @entity26 equilibrium studies, and isoelectric focusing (IEF). In the presence of oxy @entity16920 (pH 7.35, 0.05 M @entity1391 ), the fluorescence emission maximum (excitation at 420 nm) of @entity29404 immediately shifts from 587 nm ( @entity29404 alone) to 594 nm, as expected when binding to protein. The fluorescence intensity increases with time and is correlated with the @entity29404 : @entity16920 mole ratio. A slow, time-dependent reaction is also observed with microcalorimetry: the rate of heat of reaction exhibits both a fast and a slow component. The heats of reaction range from -2.1 to -14.8 mcal depending upon the @entity29404 : @entity16920 ratio of 4:1 (0.4 mM:0.1 mM) to 38:1 (3.8 mM:0.1 mM), respectively, and are typical of weak, noncovalent protein-ligand interactions. The optical difference spectra are a function of the @entity29404 : @entity16920 molar ratio and also exhibit a slow increase in intensity over time. No time-dependent optical difference spectra are observed with @entity29404 or with @entity16920 alone. The @entity26 affinity of @entity16920 in the presence of @entity29404 decreases with increasing mole ratio. During IEF, all @entity29404 separates from @entity16920 , consistent with a weak, noncovalent interaction at a non- @entity1446 pocket site. We conclude that @entity29404 binds to intact, tetrameric hemoglobin at non- @entity1446 pocket sites in a nonspecific, weak, noncovalent interaction.
