Degradation of abnormal proteins in intact mouse reticulocytes: accumulation of intermediates in the presence of bestatin.

Abstract

Incubation of intact mouse reticulocytes with bestatin (a competitive inhibitor of aminopeptidases [from Streptoverticillium olivoreticuli]) produced the accumulation of low MW intermediates in the degradation of puromycinyl-peptides or analog-containing proteins that had been pulse labeled with L-[I-14C]leucine. A large fraction of the radioactive protein was degraded to trichloroacetic acid-soluble products within 10 min. In the presence of bestatin (0.5 mg/ml), 1/4 of the products appeared to be dipeptides, tripeptides, or both: they were resistant to ninhydrin at acid pH (a treatment that decarboxylates only free amino acids) except after intensive acid hydrolysis, and they eluted from a Sephadex G-10 column with an apparent average size of 300 daltons. These radioactive products did not appear if incorporation of the tracer was prevented by prior treatment with cycloheximide, demonstrating that they originated from polypeptide precursors.