Hexokinase (HK) from yeast is 486 amino acid containing enzyme with a α/β fold. It comprises a large and small domain separated by an active site cleft. Conserved glycine residues are essential for the ATP and glucose binding. The two isoforms are HKI and HKII encoded by HXK1 and HXK2 gene, respectively.
Catalyzes the phosphorylation of D-hexose sugars at the C6 position utilizing ATP as a phosphate source.
The rate of phosphorylation varies with different hexoses (pH 7.5, 30 °C).
D-fructose KM: 0.33 mM
D-glucose KM: 0.12 mM
D-mannose KM: 0.05 mM
Yeast hexokinase exists as two similar isoforms, PI and PII (A and B), with isoelectric points of 5.25 and 4, respectively.
Molecular Weight: ~ 54 kDa (monomer)
~110 kDa (dimer)
Optimal pH: 7.5 to 9.0
Extinction Coefficient: E1% = 8.85 (PI) and 9.47 (PII) at 280 nm
Activators: Hexokinase requires Mg2+ ions (KM = 2.6 mM) for activity. Hexokinase is activated by catecholamines and related compounds.
Inhibitors: sorbose-1-phosphate, polyphosphates, 6-deoxy-6-fluoroglucose, 2-C-hydroxy-methylglucose, xylose, lyxose, and thiol reactive compounds (Hg2+ and 4-chloromercuribenzoate)
Hexokinase II is a crucial enzyme in glucose metabolism. Deletion of gene in S. cerevisiae in the presence of high glucose displays oxidative growth and results in the production of high biomass as well as shortened diauxic shift. Hexokinase II is also involved in glucose repression.