Digitonin resistance of liver mitochondria isolated from copper-deficient and copper-loaded rats.

Liver mitochondria of copper-deficient and copper-loaded rats are with changed composition, ultrastructure and functions. The aim of the present work is to study the digitonin resistance of these mitochondria as an indicator for the changes in the membranes. Copper deficiency and copper loading are achieved by eliminating resp. by adding copper to the diet for four to six weeks. The copper content of the mitochondria in the control group of animals is 0.55 X 10(-9)M/mg protein. 0.20 X 10(-9) M/mg protein in the copper-deficient rats and 1.8 X 10(-9) M in the copper-loaded rats. Digitonin resistance is measured by the degree of increase in the activity of a matrix enzyme, malatedehydrogenase, upon destruction of the various mitochondrial membranes and to a different degree by ascending digitonin concentrations. The digitonin effect on the membranes is maximal for concentrations of 0.8 to 1.0 mg digitonin/mg protein. The digitonin resistance of the inner membranes increases in the case of copper deficiency, while coppor loading has the opposite effect on the resistance of the outer membranes. Moreover, coppor loading results in an increase in the general activity of the mitochondrial malatedehydrogenase as compared with the control mitochondria.