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Small mol: BPG locks hemoglobin

bis-phosphoglycerate (BPG) is a molecule that is synthesized by red blood cells. Your blood cells produce differing amounts of BPG in response to environmental conditions; pregnant women make more, for example. Increasing production of BPG is also one element of the gradual adaptation to high altitude living.

BPG's primary feature is that it's a small molecule bearing two phosphate groups (PO42-), and thus a lot of negative charge. Initially, BPG rests in a welcoming pocket of the oxygen-releasing form of hemoglobin.

Use the following buttons to compare the BPG binding 'pocket' in the deoxy (blue) vs. oxy (red) states

Let's take a closer look at the pocket where BPG sits (deoxy form) or can't get in (oxy form). Use these controls to explore:

Highlight the following amino acids to answer the questions in the exercises:

Use the different conformations and the two labeling formats to answer the questions in the exercises.

The following can be used to answer a separate question about fetal hemoglobin: One way a fetus manages to steal oxygen from its mother's blood indirectly involves BPG. Fetuses use a different beta-globin gene which has several changes from the adult form. One of these is a change in the amino acid called for at position 143. Unlike the histidine shown, fetal hemoglobin would have a serine. Click the checkbox below to highlight this position. amino acid changed in fetal hemoglobin

When checked, atoms still present in the serine found at this position are in yellow; those missing are shown small and green. This not only means the sidechain ends further from the BPG, but the terminal hydrogen is less charged than that on tho original histidine.