JBC, Vol. 250, Issue 15, 5774-5761, Aug, 1975
Preparation of a homogeneous soluble D-beta-hydroxybutyrate apodehydrogenase from mitochondria
H. Bock and S. Fleischer
D-beta-Hydroxybutyrate dehydrogenase of bovine heart mitochondria has been
purified to apparent homogeneity. The membrane-bound enzyme is first
released by phospholipase A digestion of the mitochondria. Lithium bromide,
0.4 M, is used to aid release, and dithiothreitol is required to stabilize
the enzyme. The membranous material is removed by centrifugation, and the
apoenzyme is recovered in the supernatant and precipitated with ammonium
sulfate to 50 percent of saturation. The main purification (100-fold) is
achieved by selective adsorption and elution on controlled pore glass
beads. The purified enzyme has been purified approximately 250-fold from
the mitochondria. The purified enzyme is homogeneous as shown by
poly-acrylamide gel electrophoresis in sodium dodecyl sulfate or acid-urea
systems; a sharp band is obtained which is equivalent to a subunit
molecular weight of 31,500. The apoenzyme is devoid of lipid and is
completely inactive as isolated. It can be reactivated by adding aqueous
microdispersions of lecithin or phospholipids containing lecithin. The
apoenzyme is stable, i.e. it has a half-life of about 450 hours at 0-2
degrees in 0.4 M lithium bromide, containing 5 mM dithiothreitol at pH 7,
and is soluble at these conditions, existing mainly as a monomer and dimer
in dilute solution. It has a tendency to associate into larger aggregates
when the salt concentration is lowered. The enzyme does not have a
distinctive amino acid composition as compared with other proteins or
soluble dehydrogenases. The purified apodehydrogenase is well suited for
study of specific protein-lipid interaction, as well as the molecular basis
for the role of phospholipid in this lipid-requiring enzyme.