- When muscles exercise, they create lactic acid which lowers the pH of the blood.
- Hemoglobin’s affinity for oxygen less, so it releases 10% more oxygen at the lower pH in the muscles. 
- CO2 also assists oxygen binding to the hemoglobin by binding to the hemoglobin as a carbamate. And the T state of hemoglobin binds more CO2 in the carbamate form than the R state. 
- The protons released by carbamate formation promotes release of oxygen release through the Bohr effect. 


The Bohr Effect: Exercising

- Conformational changes in the receptor cause pH changes in the blood stream which shows the need for a blood buffer system. 
- In physiological conditions, hemoglobin releases protons once oxygen binds, and it decreases the pH in the blood. It causes hemoglobin to bind less oxygen. This is known as the Bohr effect after Christian Bohr. 
- Physiologically, it is key in transporting oxygen from the lungs to the tissues and then moving CO2 from the respiration to the lungs (See figure). 
- CO2 made in the tissues moves  to the capillaries and dissolves to form bicarbonate (HCO3-) slowly (See figure). 	
- RBC contains carbonic anhydrase that accelerates the reaction so most of the CO2 in the blood is carried as bicarbonate (to prevent CO2 bubbles in the blood) (See figure). 


Grand Valley State University

-  The T-state is the hemoglobin conformational state of deoxyhemoglobin, or the hemoglobin without oxygen bound.
- The iron is situated 6 Angstroms out of the heme and allows for the iron to access oxygen. 


T-State of Hemoglobin

- R-state is the conformational state of oxyhemoglobin.
- When oxygen binds, it “flattens” the iron complex. 
- To prevent steric clash during flattening of the heme, there is an alpha helix that tilts as well.
- Overall, changes in hemoglobin's conformational states at the tertiary level cannot occur without causing quaternary structure changes in the whole protein. 

R-State of Hemoglobin

Voet, D., Voet, J. G., & Pratt, C. W. (2013). Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contractions, and Antibodies. In Fundamentals of biochemistry: Life at the molecular level (4th ed., pp. 176-216). Hoboken, NJ: Wiley. Retrieved February 21, 2021, from archive.org.

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