CHARACTERIZATION OF MITOCHONDRIA FROM PIG MUSCLE - HIGHER ACTIVITY OFEXO-NADH OXIDASE IN ANIMALS SUFFERING FROM MALIGNANT HYPERTHERMIA

Mitochondria were isolated from biopsies of the biceps femoris muscle of Danish landrace pigs. Three groups of animals were compared: (1) no rmal pigs; (2) pigs that were homozygous with respect to the gene Hal( n)/Hal(n) coding for the porcine malignant hyperthermia syndrome; and (3) heterozygote animals. A newly developed micro-method for preparati on and assaying of small quantities of intact mitochondria was employe d. With this technique mitochondria from biopsies weighing less than 1 00 mg were examined with respect to cytochrome content as well as phos phorylating and respiratory activities, including the nonphosphorylati ng exo-NADH oxidase activity. The mitochondria, prepared in a yield of 48 %, showed high respiratory activities with tricarboxylic acid-cycl e intermediates and pyruvate, and somewhat lower activity with palmito yl-carnitine as substrate. The ATP synthase activity was about 1000 mu mol ATP/min per g of protein and the maximal respiratory activity app rox. 700 mu mol of O-2/min per g of protein. No differences among the three groups of animals were detected, except for the exo-NADH oxidase activities, which were 43, 78 and 107 mu mol of O-2/ min per g of pro tein in the groups of normal, heterozygous and homozygous animals resp ectively. It is concluded that the exo-NADH oxidase activity may be a genetic manifestation of malignant hyperthermia and may play a signifi cant role in the heat production characteristic of the syndrome.