|Topic:||Phosphoglycerate Kinase .|
|Details:|| The high-energy phosphate of 1,3-BPG is used to form ATP and 3-phosphoglycerate (3PG) by the enzyme phosphoglycerate kinase (PGK). Note that this is the only reaction of glycolysis or gluconeogenesis that involves ATP and yet is reversible under normal cell conditions. There are two PGK genes in humans identified as PGK1 and PGK2. The PGK1 gene is located on the X chromosome (Xq21.1) and is composed of 11 exons encoding a protein of 417 amino acids. The PGK2 gene arose through a retrotranspositional event with the PGK1 gene and it is expressed only in the testis. The PGK2 gene is an intronless gene located on chromosome 6p12.3 and it encodes a protein of 417 amino acids. The PGK2 encoded protein shares 87% identity to the PGK1 encoded protein.
Associated with the phosphoglycerate kinase pathway is an important reaction of erythrocytes, the formation of 2,3-bisphosphoglycerate, 2,3BPG (see Figure below). 2,3BPG is an important regulator of the affinity of hemoglobin for oxygen. The synthesis of 2,3BPG, as well as its degradation to 3-phosphoglycerate, is catalyzed by the bi-functional enzyme 2,3-bisphosphoglycerate mutase (BPGM). The two activities of BPGM are 2,3-bisphosphoglycerate synthase, and 2,3-bisphosphoglycerate phosphatase. The synthase activity of the enzyme is most active at alkaline pH, whereas, the phosphatase activity is more active at acidic pH. BPGM is structurally related to the phosphoglycerate mutase (PGAM) isozymes described in the next section but is encoded by a distinct gene. The BPGM gene is located on chromosome 7q33 and is composed of 6 exons that generate three alternatively spliced mRNAs, each of which encode the same 259 amino acid protein.
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