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]
Enzymatic reaction of: galactokinase
EC Number: 22.214.171.124α-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] 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]
pH(opt): 7.3 [Dey83]
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