u-p-Hydroxybutyric Dehydrogenase of Mitochondria*

Although the reversible oxidation of free n-/3-hydroxybutyrate to acetoacetate in animal tissues was first observed many years ago (1, 2), relatively little is known about the properties and intracellular distribution of the dehydrogenase responsible for this reaction. In 1937 Green et al. (3) described a stereospecific diphosphopyridine nucleotide-linked n-P-hydroxybutyric dehydrogenase in respiratory particles from pig heart, distinct from lactic and malic dehydrogenases. The enzyme was also demonstrated to be present in liver mitochondria (4, 5) and the one-step DPN-linked oxidation of n-/?-hydroxybutyrate to acetoacetate has been frequently used to study properties of the respiratory chain and of phosphorylations coupled to DPN-linked electron transport (4-7). In addition, McCann (8) has demonstrated oxidation of both stereoisomers of P-hydroxybutyrate by the mitochondria of a number of other normal tissues, and Emmelot and Bos (9) have shown oxidation of the n-isomer by mitochondria of certain tumors. This paper describes the assay and some kinetic properties of the dehydrogenase, its occurrence in various tissues and subcellular structures, and the role of mitochondrial structure in the activity of the enzyme. The experiments also provide evidence of some factors affecting the accessibility of DPN to the mitochondrial dehydrogenase.