LYSOSOMES IN SKELETAL MUSCLE TISSUE Zonal Centrifugation Evidence for Multiple Cellular Sources

Postnuclear supernates from homogenates of skeletal muscle from rats subjected to starvation, injections of Triton WR-1339, dextran-500, and dextran + corticosterone were fractionated by means of rate and isopycnic zonal centrifugation in sucrose-0 .02 M KCl gradients . Zonal fractions were analyzed for protein, RNA, cytochrome oxidase, and up to six acid hydrolases . The results indicate the presence of two groups of lysosome-like particles . One group contributes approximately 95% of the cathepsin D and acid phosphatase activity and 75% of the acid ribonuclease, ß-glucuronidase, and arylsulfatase activity in muscle . It is characterized by a modal equilibrium density of 1 .18 that is .decreased by starvation, but is not shifted by dextran-500 or Triton WR-1339 . The second group has a higher proportion of acid ribonuclease, ß-glucuronidase, and arylsulftase ; the equilibrium density can be shifted by dextran-500 and Triton WR-1339. It is suggested that this group of lysosomes is derived from macrophages and other connective tissue cells, whereas the former group represents lysosome-like particles from muscle cells .