Preparation and partial purification of soluble choline dehydrogenase from liver mitochondria.

Choline dehydrogenase is the initial enzyme of the complete choline oxidase system. The latter includes all agents and enzymes involved in hydrogen transport to oxygen plus the initial dehydrogenase. Problems concerning the properties of choline dehydrogenase have remained unsolved largely because of the insoluble nature of the enzyme. It has resisted solution by such techniques as freezing and thawing (Williams, 1952) and extraction of acetonepowders of rat-liver mitochondria (Williams & Sreenivasan, 1953). The latter authors extracted the enzyme from acetone powders of mitochondria with the use of bile salts, but it could not be redissolved once the bile salts were removed. It became clear that further treatment or alternative methods would be required to obtain the enzyme in a truly soluble form. The term 'soluble' is arbitrarily defined as remaining in the supernatant fluid after centrifuging at 144 000 g for at least 60 min. and capable of redissolving in aqueous media without the use of dispersing agents, after precipitation with substances (e.g. ethanol) which do not inactivate the enzyme. In the present paper we describe a method for preparing the enzyme in a form which meets these qualifications of solubility.