Lysosomal enzyme activity in rat and beef skeletal muscle.

Abstract

Abstract 1. 1. Acid hydrolases (β-glucuronidase EC 3.2.31; cathepsin; β-galactosidase EC 3.2.1.23; ribonuclease EC 2.7.7.17) of rat and beef skeletal muscle are associated with cytoplasmic particles and are poorly reactive towards external substrates; however, their activity is enhanced or even fully displayed by injuring the particles with a variety of treatments (osmotic shock, sonication, alternate freezing and thawing, addition of Trition X-100). 2. 2. By gradually increasing the concentration of Triton X-100 in the enzyme assays, acid hydrolases are gradually liberated from the particles, more homogeneously from those of rat than of beef muscle. 3. 3. Osmotic and thermal treatments of beef skeletal lysosomes reveal a higher stability of the particles as compared to those from liver and kidney. 4. 4. The 4 hydrolytic enzymes display in the sedimented of fractions a very similar distribution pattern, different from that of cytochrome c oxidase and NAD glycohydrolase. Highest relative specific activity of lysosomal enzymes was found associated to a post-mitochondrial fraction. 5. 5. By isopicnic centrifugation of a post-mitochondrial fraction, both from rat an beef muscle, acid hydrolases were broadley distributed throught the water surcrose gradient (d = 1.10−1.20); cytochrome c oxidase was in a narrow band and NAD glycohydrolase showed a bimodal distribution. 6. 6. On the basis of sedimentation coefficient and equilibrium density acid hydrolases of skeletal muscle are associated to particles different from mitochondria. and microsomes. The homogenous properties of these enzymes suggest that they are associated with a single functional form of lysosome-like particles.