Intracellular distribution of choline oxidase.

Recently considerable attention has been centered upon the relation of choline oxidase activity to folic acid, the Leuconostoc citrovorum factor (LCF), ascorbic acid, and vitamin B,,. From this laboratory it has been indicated that rat liver choline oxidase can be stimulated in vitro under certain conditions by these factors, especially if the activity of the enzyme is previously decreased by dietary aminopterin (l-3). In beginning a more detailed study of the prosthetic group of choline oxidase, the present experiments were carried out to locate the activity of the enzyme in one of the fractions of rat liver, by means of Schneider’s method of differential centrifugation (4). In this way it could be determined whether choline oxidase is associated with the nuclei, mitochondria, microsomes, or the supernatant, or whether a combination of two or more fractions is necessary for the enzymatic activity. Quite recently Swendseid et al. (5) have reported the intracellular distribution of vitamin B12, folic acid, and LCF in mouse liver. In view of that work and the previous investigations relating these factors to choline oxidase, it was of interest to determine whether the distribution of the enzyme follows the distribution of these factors in the liver fractions.