J. Biol. Chem., Vol. 261, Issue 21, 9572-9575, Jul, 1986
Rabbit muscle extracts catalyze the specific removal of N- acetylmethionine from acetylated peptides
G Radhakrishna and F Wold
Rabbit muscle has been found to contain an activity that catalyzes the
specific removal of Ac-Met from acetylated peptides. The activity is
associated with free ribosomes and microsomes in the rabbit muscle extract
but can be removed from these subcellular fractions by exposure to 0.5 M
NaCl in the presence of 2 mM MgCl2; only partial removal was achieved with
microsomes, but complete removal with ribosomes. A nearly 200-fold
enrichment of the activity was achieved by this simple succession of
differential centrifugation and salt extraction. Eighteen
14C-acetylpeptides have been tested as substrates for the partially
purified activity assaying for the production of free 14C-acetylamino acid
by high performance liquid chromatography. None of the peptides containing
N-terminal acetylated Ala, Asp, Ser, or Gly were cleaved at a significant
rate. Six of a total of eight peptides containing N- terminal Ac-Met were
cleaved by the ribosomal extract at different rates. The active substrates
varied in length from tri- to undecapeptides. The activity is inhibited by
high concentrations of the protease inhibitor phenylmethylsulfonyl
fluoride. Based on these observations, we tentatively conclude that the
activity satisfy the criteria of a general N-terminal protein processing
enzyme: it can remove Ac-Met from most, but not all, N-terminal sequences
and appears to be inactive toward the N-terminal acetylamino acids most
commonly found in eukaryotic proteins.