The degree of control exerted by the mitochondrial choline transporter over the choline oxidation pathway was measured in isolated rat liver mitochondria. Choline transporter activity was titrated with hemicholinium-3, a known competitive inhibitor of the transporter. It was shown that the rate of betaine efflux from mitochondria was an accurate measure of choline oxidation. The relative rate of choline oxidation was measured as a function of the relative degree of inhibition of the transporter. The resulting data gave a flux control coefficient over choline oxidation of 0.9 for the choline transporter. It is concluded that the choline transporter is the major site for control of choline oxidation in isolated rat liver mitochondria.
