Purification and properties of galactokinase from pig liver

Abstract

Galactokinase has been purified from the liver of young pigs by high-speed centrifugation, chromatography on Sephadex G-100 and diethylaminoethyl-cellulose, and (NHy)2 SO4 fractionation. The enzyme preparation has a specific activity of 10-18 [mu] moles of galactose phosphorylated/mg of protein/min. at 37[degree] and has been purified 400-fold from the liver supernatant. Purified liver galactokinase has Michaelis constants of 1x10-4-3x10-4 [image] for galactose and 2x10-4 [image] for ATP-Mg2+, and the enzyme reaction produces equimolar amounts of galactose 1-phosphate and ADP. Galactokinase phosphorylates 2-deoxygalactose and galactosamine in addition to galactose, has a pH optimum of 7-8, a Q10 of 2, and is stimulated by cysteine and other thiols. With the exception of substrate specificity, the properties of liver galactokinase are similar to galactokinase purified from yeast and Escherichia coli.