STRUCTURAL CHANGES ASSOCIATED WITH THE RELEASE OF ENZYMES FROM RAT-LIVER MITOCHONDRIA BY FREEZING

Abstract

Suspensions of rat-liver mitochondria in 0.44 M sucrose, after they were frozen and thawed under defined conditions, were partitioned into three sedimentable and one supernatant fraction by differential centrifugation. These were analyzed for optical density, protein content, and for activities of glutamate dehydrogenase (GD) and 3-hydroxybutyrate dehydrogenase (BD) with exogenous nicotinamide–adenine dinucleotide (NAD) both as maximum activity after sodium deoxycholate treatment and as activity released by freezing. Pellets of the three sedimentable fractions were also examined in the electron microscope. When dehydrogenases were not released by a freezing treatment, no structural changes were detected. Release of BD, which was accompanied by release of GD as well, was associated with mitochondrial disruption and drastic rearrangement of mitochondrial membranes. On the other hand, release of GD without BD occurred from swollen and emptied mitochondria. The partial release of enzymes in a preparation was not associated with a partial structural modification of all of the mitochondria, but rather with drastic structural changes in only some of them.