None of the glycolytic reactions require oxygen as a cofactor. So, why do low-oxygen conditions (hypoxia) impact glycolysis? Under hypoxic conditions, ATP cannot be synthesized by substrate-level phosphorylation. Under hypoxic conditions, enolase cannot remove a molecule of water from 2-phosphoglycerate. Under hypoxic conditions, aldolase cannot cleave a hexose molecule into two triose molecules. Under hypoxic conditions, NADH cannot be reoxidized to NAD+ by passing its electrons to oxygen.