Choline Kinase from Brewers’ Yeast

Choline kinase was purified approximately 300-fold, in 5% yield, from an autolysate of dried brewers’ yeast. A molecular weight of 67,000 was estimated using a Stokes radius of 33 A, as determined by Sephadex G-200 chromatography. An s~,,,~ of 4.8 S was obtained by sucrose density gradient centrifugation. Enzyme activity was diminished by sulfhydryl inhibitors and stabilized by the presence of magnesium ion. The Michaelis constant for ATP was 1.4 x 10e4 M. The Michaelis constant with respect to choline was 1.5 X low5 M at low choline concentrations; reciprocal plots at high choline concentrations were nonlinear. Initial velocity and product and dead-end inhibitor studies were performed on the forward reaction and were consistent with a Random Bi-Bi mechanism for catalysis.