After Releasing O2 at the Tissues Hemoglobin Transports CO2 Protons to the Lungs

In addition to transporting O2 from the lungs to peripheral tissues, hemoglobin transports CO2, the byproduct of respiration, and protons from peripheral tissues to the lungs. Hemoglobin carries CO2 as carbamates formed with the amino terminal nitrogens of the polypeptide chains.

Carbamates change the charge on amino terminals from positive to negative, favoring salt bond formation between the a and P chains.

Hemoglobin carbamates account for about 15% of the CO2 in venous blood. Much of the remaining CO2 is carried as bicarbonate, which is formed in erythrocytes by the hydration of CO2 to carbonic acid (H2CO3), a process catalyzed by carbonic anhydrase. At the pH of venous blood, H2CO3 dissociates into bicarbonate and a proton.

Deoxyhemoglobin binds one proton for every two O2 molecules released, contributing significantly to the buffering capacity of blood. The somewhat lower pH of peripheral tissues, aided by carbamation, stabilizes the T state and thus enhances the delivery of O2. In the lungs, the process reverses. As O2 binds to deoxyhemo-globin, protons are released and combine with bicarbonate to form carbonic acid. Dehydration of H2CO3, catalyzed by carbonic anhydrase, forms CO2, which is exhaled. Binding of oxygen thus drives the exhalation of CO2 (Figure 6-9).This reciprocal coupling of proton and O2 binding is termed the Bohr effect. The Bohr effect is dependent upon cooperative interactions between the hemes of the hemoglobin tetramer. Myo-globin, a monomer, exhibits no Bohr effect.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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