Activation and inhibition of rat liver L-threonine dehydrogenase

We have studied some characteristics of mitochondrial rat liver L-threonine dehydrogenase during freezing: the enzyme shows a net increase in activity and a "shift" in the pH optimum after storage at -20 degrees C of mitochondrial preparations. An unknown effector, which inhibited significantly the dehydrogenase activity, was isolated from the same preparations kept for 7-10 days at -20 degrees C. Some properties of the inhibitor have been determined.