Interaction of d-β-hydroxybutyrate dehydrogenase with lecithin vesicles

Rat liver mitochondrial d-β-hydroxybutyrate dehydrogenase has an absolute requirement for lecithin. The nature of the interaction between the enzyme and phospholipid has been investigated. Single bilayer lecithin liposomes of shell-like structure bring about maximal enzyme activation, whereas the interaction with larger vesicles leads to enzyme inactivation. The strong binding of the enzyme to lecithin confers great stability to the enzyme activity as compared with the nonlipid-activated enzyme, and permits the isolation of a lipoprotein complex by chromatography on Sephadex G-200. Only 20% of the proteins solubilized with d-β-hydroxybutyrate dehydrogenase from mitochondrial membranes bind to lecithin liposomes, thus a 5-fold purification of the enzyme is achieved. The liposome-bound proteins had a significantly lower polarity than the remaining 80% of solubilized mitochondrial membrane proteins.