1. [n]  the smallest whole number or a numeral representing this number; "he has the one but will need a two and three to go with it"; "they had lunch at one"
2. [adj]  used of a single unit or thing; not two or more; "`ane' is Scottish"

1,3BPG is also responsible for the production of an allosteric effector of hemoglobin, 2,3-bisphosphoglycerate (2,3BPG). In this reaction, a phosphoryl group is transferred from 1,3BPG to the C-2 of 3PG. This yields 2,3BPG and a different 3PG molecule.