Abstract
In order to determine the effects of lysosomal enzymes on muscle proteins, fragmented sarcoplasmic reticulum was obtained from rabbit longissimus muscle and incubated with cathepsin B1 for 2 hr at 25° C and 18 hr at 2° C each at pH 6.8 and 5.8. Following incubation calcium uptake and ATPase activity of the vesicles were measured. Differences in the physical structure of the vesicles were determined using electron microscopy and differences in molecular weight and subunit structure of the proteins associated with the sarcoplasmic reticulum were determined by sodium dodecylsulfate polyacrylamide gel electrophoresis. A significant (P<0.05) decrease in calcium uptake was observed at the 2 hr incubation while a highly significant (P<0.01) decrease was found during the 18 hr incubations. The ATPase activity was inhibited only by the pH 5.8, 18 hr incubation. Gel electrophoresis shows a loss of the protein associated with ATPase activity following the 2 hr, pH 5.8; 18 hr, pH 5.8 and 18 hr, pH 6.8 incubations. These data seem to indicate that certain easily digestible proteins are responsible for the permeability of the membrane and calcium uptake whereas the ATPase protein does not appear to be as accessible to the proteolytic enzyme. The protein associated with the ATPase activity was purified and incubated at pH 5.8 for time periods of 1, 60, and 120 min. Loss of ATPase activity and degradation as indicated by gel electrophoresis was observed at all time periods. Differences in the vesicles using electron microscopy were detectable only at the 18 hr, pH 5.8 incubation. There was a loss of the surface particles and a disruption of the membrane surrounding the vesicles.
Fields, Phillip Arthur (1976). Proteolysis of the sarcoplasmic reticulum by cathepsin B1. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -508364.