Hemoglobin is the protein that transports oxygen in our blood. In the structure shown in the initial view (), all four heme groups bind to oxygen . Two amino acid side chains are covalently bound to sugar molecules in a type of modification called glycated. This happened because the protein experienced high sugar levels for a long time. The sugar is is labeled fructose, but it originated from glucose. Glucose forms a glycosidic bond with the nitrogen atom of the sidechain of lysine. Then, it dehydrates to a Schiff base and undergoes Amadori rearrangement[3] (a shift in the double bond) to fructose. In hemoglobin from patients with untreated diabetes, the modifications include glucose linked to the amino terminal groups of the alpha and beta chains as well as by glucose. The HbA1c test [4]specifically tests for the modification of the (not modified in this structure).
