Influence of pH on Bovine Hemoglobin - METTLER TOLEDO

Influence of pH on Bovine Hemoglobin

Samples

Bovine whole blood, stabilized with citrate

 

Conditions

Measuring cell: DSC20

Pan: Aluminum standard 40 µl, hermetically sealed

Reference: Approximately the same amount of water

Sample preparation: Destroying the cells by freezing. The native pH is 7.06, the adjustment has been done with 0.5 mol/l HCl.

DSC measurement: Heating from 30 °C to 110 °C at 10 K/min


Interpretation

The actual pH value and whether it is kept constant or changes has a large influence on the course of the process and the product quality.

In the present measurement, the main protein component of the red blood corpuscles, hemoglobin, is exposed to different pH values. The globin chains, which are a protein fraction of the hemoglobin molecule, are denatured on heating.

The physiological pH value of the blood is 7.35. In this state, the hemoglobin can not be measured because it immediately coagulates. A value of 18 J/g is assumed to be the native denaturation enthalpy measured with addition of a small amount of citrate at pH 7.06.

When the pH is lowered to a slightly acidic value (pH 5.8), the enthalpy shows no significant decrease, but the peak maximum is shifted to lower temperatures. In other words the pH value influences the thermic stability of the protein.

Heme stabilizes the structure of hemoglobin. In an acidic denaturation, the molecule becomes unstable and hence more sensitive to heat. A significant feature is the lowering of the temperature of the peak maximum. Moreover the peaks become broader. At pH 4.28 the molecule unfolds, but the heme is still attached to the globin chains. Only a very small enthalpy change can be measured and the reaction takes place at much lower temperatures (60 °C to 70 °C).

In the acidic pH range (pH 3.3), the sample is already fully denatured, i.e. uncoiled as a result of the high hydrogen ion concentration, so that the thermic treatment of the DSC measurement induces no further reaction. Only a straight baseline is recorded.

 

Evaluation


Conclusion

 

Influence of PH on Bovine Hemoglobin | Thermal Analysis Application No. HB 1009 | Application published in METTLER TOLEDO TA Application Handbook Food