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MJ Lin, RL Nagel and RE Hirsch
Department of Medicine, Albert Einstein College of Medicine, Bronx, NY.
We previously reported that circulating hemoglobin (Hb) CC erythrocytes
contain oxygenated HbC crystals with little or no HbF and that HbF inhibits
in vitro crystallization of HbC. We now report that HbS accelerates in
vitro crystallization of HbC. Crystals were formed in 1.8 mol/L potassium
phosphate buffer, pH 7.4, at 30 degrees C and were counted in several time
intervals with a hematocytometer. The hemoglobin composition of
Millipore-isolated crystals and supernatant were also analyzed. Under the
conditions selected, 100% HbS formed needle-shaped crystals only after two
hours. Pure HbC does not form crystals within 15 minutes, whereas a ratio
of 10% HbS:90% HbC forms 1,100 crystals/mm3, 20% HbS:80% HbC forms 370
crystals/mm3, and 30% HbS:70% HbC forms 5 crystals/mm3. Crystals formed in
the presence of HbS are tetragonal, as are pure HbC crystals. As compared
with 100% HbC, HbA or albumin mixed with HbC showed a decreased number of
crystals as a result of dilution. Analysis of the Hb content of isolated
crystals by citrate agar gel electrophoresis showed that HbS was rapidly
incorporated into the crystal in the same ratio over time. These results
demonstrate that HbS accelerates crystallization of HbC with respect to the
rates of crystallization of any of these two Hbs separately, through a
mechanism that involves cocrystallization. These results may be significant
in understanding SC disease.
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