MetaCyc Enzyme: galactokinase

Synonyms: galactose kinase

Species: Vicia faba

Subunit composition of galactokinase = [galactokinase]2

Galactokinase is the first committed enzyme of the Leloir pathway of D-galactose metabolism ( D-galactose degradation I (Leloir pathway)). It allows the conversion of galactose into galactose-1-phosphate. Galactose-1-phosphate is known to be interfere with the metabolism of D-hexoses and is a possible cause of galactose toxicity in plants; it has therefore been proposed that galactokinase plays an important role in the regulation of hexose metabolism. The enzyme purified from Vicia faba was shown to use ATP as efficient phosphate donor; CTP, GTP and UTP are not effective substitutes [Dey83]. The enzyme was also shown to require metal ions (Mg2+ > Co2+ > Mn2+ > Ni2+ > Ca2+) for activity whereas heavy metals ions and sulphydryl reagents were inhibitory, indicating the participation of -SH group(s) in the enzymatic reaction [Dey83].

Molecular Weight of Polypeptide: 30.9 kD (experimental) [Dey83]

Molecular Weight of Multimer: 60 kD (experimental) [Dey83]

pI: 5.3 [Dey83]

Gene-Reaction Schematic

Gene-Reaction Schematic

Enzymatic reaction of: galactokinase

Inferred from experiment

EC Number:

α-D-galactose + ATP → α-D-galactose 1-phosphate + ADP + H+

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the Enzyme Commission system.

This reaction is reversible.

Alternative Substrates for α-D-galactose: 2-deoxy-D-galactose [Dey83], D-galactosamine [Dey83]

In Pathways: D-galactose degradation III, D-galactose degradation I (Leloir pathway)

Activators (Unknown Mechanism): Mg2+ [Dey83], Co2+ [Dey83], Mn2+ [Dey83] Inhibitors (Competitive): α-D-galactose 1-phosphate [Dey83] Inhibitors (Noncompetitive): ADP [Dey83] Inhibitors (Unknown Mechanism): Cu2+ [Dey83], Zn2+ [Dey83], Hg2+ [Dey83]

Primary Physiological Regulators of Enzyme Activity: Mg2+, Mn2+, ADP, α-D-galactose 1-phosphate

Kinetic Parameters:
Substrate Km (μM) Citations
α-D-galactose 1500.0 [Dey83]
ATP 500.0 [Dey83]

pH(opt): 7.3 [Dey83]


Dey83: Dey PM (1983). "Galactokinase of Vicia faba seeds." Eur J Biochem 136(1);155-9. PMID: 6617655

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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