Hypoxia-dependent regulation of key metabolic enzymes. (a) Reverse transcription - Polymerase Chain Reaction (PCR) results from PC12 cells grown either in hypoxic or normoxic conditions. The transcript levels are studied for enzymes pyruvate kinase (PK), hexokinase (HK), phosphofructokinase (PFK), citrate synthase (CS), Glyceraldehyde dehydrogenase (GAPDH), and β-actin (as internal control). (b) The kinetics of HK mRNA and protein levels according to the classical model under normoxic and hypoxic conditions (normoxia = 7 mM O2, hypoxia = 0.35 mM O2) as an example of hypoxia-responsive gene expression in the model. HK mRNA production kinetics in astrocytes (An) under normoxic and hypoxic condition is shown on the left panel, and HK protein production kinetics in astrocytes (Ac) under normoxic and hypoxic condition is shown on the right panel. (Please note that all hypoxia-responsive genes have same rate equations, thus the same kinetic profiles in the model).