Biochemical characterization of mitochondrial and lysosomal particles in old rat liver

Sedimentation rates, equilibrium densities, and membrane fragility of liver mitochondrial and lysosomal particles were estimated in adult and 36-month-old rats. The sedimentation coefficient and the size of particles were also calculated. The fractionation experiments indicated a similar enzymatic distribution for mitochondrial and lysosomal tracer enzymes in both types of animals. The liver mitochondria of senescent and mature rats were identical in sedimentation rate, sedimentation constants, equilibrium densities, fragility under isotonic conditions, and oxidative phosphorylation. Only in hypotonic media was there a decreased cohesiveness of the external mitochondrial membrane in older animals. In old rats several lysosomal tracer enzymes had lower sedimentation rates and sedimentation coefficients. The equilibrium densities were higher in these animals too. The lysosomal latency in old and mature rats was identical. It can be concluded that in very old age liver lysosomes are smaller in size than those in mature animals.