Abstract
Choline kinase (EC 2.7.1.32) was measured in concentrated 100,000 g av supernatants from castor bean endosperm ( Ricinus communis L. var. Hale). Initial velocity analysis, along with competitive inhibitor (hemicholinium-3) and product inhibition (ADPMg 2+) studies suggested that the forward reaction followed a sequentially ordered mechanism with ATPMg 2+ binding to the enzyme first, followed by choline and then activation of the ternary complex by free Mg 2+. The kinetic constants of the forward reaction are reported. A reverse reaction was measured which had a pH optimum of 6.5 and produced 1 mol of ATP for every mole of choline phosphate. The estimated maximum possible K eq at 7.25 was 5 × 10 −3 which suggested that this reaction is highly reversible in this tissue. The possible physiological significance of this is discussed.
Published Version
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