What is the immediate donor of the phosphoryl group of ADP in the production of ATP during glucose metabolism in RBCs?

The immediate donor of the phosphoryl group of ADP in the production of ATP during glucose metabolism in Red Blood Cells (RBCs) is 1,3-bisphosphoglycerate (1,3-BPG) or phosphoenolpyruvate (PEP), depending on the specific pathway of glucose metabolism.

Here are the steps:

1. Glucose enters the RBC and is converted to glucose-6-phosphate by the enzyme hexokinase.

2. Glucose-6-phosphate is then converted to fructose-6-phosphate by the enzyme phosphoglucose isomerase.

3. Fructose-6-phosphate is converted to fructose-1,6-bisphosphate by the enzyme phosphofructokinase.

4. Fructose-1,6-bisphosphate is split into two three-carbon molecules: glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). DHAP is quickly converted to G3P, so there are two G3P molecules.

5. Each G3P is converted to 1,3-bisphosphoglycerate (1,3-BPG) by the enzyme glyceraldehyde-3-phosphate dehydrogenase. This step also generates NADH.

6. The 1,3-BPG donates a high-energy phosphate to ADP, forming ATP and 3-phosphoglycerate. This reaction is catalyzed by the enzyme phosphoglycerate kinase.

Alternatively, in the final step of glycolysis, phosphoenolpyruvate (PEP) can donate a phosphate group to ADP to form ATP and pyruvate, in a reaction catalyzed by the enzyme pyruvate kinase. This is another possible immediate donor of the phosphoryl group of ADP in the production of ATP during glucose metabolism in RBCs.