Add time:07/22/2019         Source:sciencedirect.com

The double-headed aspirin, bis(3,5-dibromosalicyl) fumarate, has been used to crosslink hemoglobin A between Lys 82β1 and Lys 82β2(J. A. Walder et al. (1979) Biochemistry18, 4265). Denaturation experiments were used to compare the stability of this crosslinked protein to that of hemoglobin A. Thermal denaturations, done in 0.01 m 4-morpholinepropanesulfonic acid, pH 7, containing 0.9 m guanidine to prevent precipitation at high temperatures, were monitored by changes in absorbance between 190 and 650 nm using a diode array spectrophotometer. The sample was heated from 25 to 70 °C at 0.3 °C/min. The data were analyzed by using both a two-state model and a novel first derivative method. As expected, methemoglobin A had a single, broad transition with a midpoint of 40.7 °C. The crosslinked methemoglobin showed a transition at 57.1 °C. Two minor transitions, one of which was apparently due to residual unmodified hemoglobin, were also observed in the crosslinked sample. Thus, a single crosslink between only two of the four subunits can lead to a significantly more stable molecule. These results can be explained by Le Chatelier's principle, since crosslinking prevents dissociation of the β-subunits and, thereby, holds the entire tetramer together.

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