Class: BE-210
Group: W3
Members: Sthita Das, Lauren Entrekin, Phillip Oh, Keith Somma
Date: April 30, 1998
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Abstract:
The purpose of this experiment was to investigate the physiological properties of hemoglobin which constitute its buffering capacity. To achieve this goal, multiple titrations were performed in order to find pK values and isoelectric points. Ovalbumin was also studied in a similar fashion to ensure the accuracy of the procedure. Using the knowledge of the amino acid content of both ovalbumin and hemoglobin, the amount of base needed to reach the pKa and the isoelectric point was determined for each buffer. These molar amounts were compared to determine which of the proteins was the superior buffer. Average pKa values were 5.43 and 3.93, while isoelectric points were 6.87 and 4.62 for hemoglobin and albumin, respectively. These values are consistent with literature values obtained from Lehninger3. It was then determined that 2.3256 mL and 5.4192 mL of NaOH needed to be added to hemoglobin and ovalbumin, respectively, to reach the pKa. According to experimental calculations, 3.3 mL and 1.47 mL of NaOH were used for hemoglobin and ovalbumin, respectively. The discrepancy in the albumin values is caused by experimental error: because the carboxyl groups were still mostly in their ionized form, much less NaOH was needed to reach pKa than expected theoretically. The hemoglobin error was caused by the ionization of the side chains of Histadine.