Evidence that lysosomes are not involved in the degradation of myofibrillar proteins in rat skeletal muscle.
To examine the role of lysosomes in the degradation of skeletal-muscle myofibrillar proteins, we measured the release of N tau-methylhistidine from perfused muscle of starved and fed rats in the presence or absence of agents that inhibit lysosomal proteinase activity. After 1 day of starvation, the release of N tau-methylhistidine by perfused muscle of 4-, 8- and 24-week-old rats increased by 322, 159 and 134% respectively. On the other hand, total protein breakdown, assessed by tyrosine release, increased by 62, 20 and 20% respectively. Inhibitors of lysosomal proteinases as well as high concentrations of insulin or amino acids failed to diminish the release of N tau-methylhistidine by perfused muscle of starved and fed rats, despite a 25-35% inhibition of total protein breakdown. The data strongly suggest that the complete breakdown of myofibrillar proteins occurs via a non-lysosomal pathway. They also suggest that total proteolysis, which primarily reflects non-myofibrillar protein breakdown, occurs at least in part within lysosomes.
B B
BB
Lowell
N B
NB
Ruderman
M N
MN
Goodman
D000818:Animals; D008247:Lysosomes / Q000378:metabolism*; D008297:Male; D008762:Methylhistidines / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013217:Starvation / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D008762:Methylhistidines; D009124:Muscle Proteins; D014443:Tyrosine; C028118:3-methylhistidine