The Journal of Cell Biology, Vol 65, 103-111, Copyright © 1975 by The Rockefeller University Press
Mitochondrial and cytoplasmic ribosomes and their activity in blood and culture form Trypanosoma brucei
J Hanas, G Linden and K Stuart
Ribosomes of Trypanosoma brucei, a parasitic, flagellated protozoan (order
Kinetoplastida), were identified on sucrose density gradients by their
radioactively labeled nascent peptides. Ultraviolet absorption revealed
only cytoplasmic ribosomes which served as internal sedimentation markers.
Synthesis on cytoplasmic ribosomes was completely inhibited by
cycloheximide. In the presence of this antibiotic, nascent peptides were
associated with ribosomes of lower sedimentation coefficient than the
cytoplasmic ribosomes. Chloramphenicol blocked synthesis on these ribosomes
which are probably the mitochondrial ribosomes. These ribosomes differed
from the cytoplasmic ribosomes in several ways. Their sedimentation
coefficient was about 72S rather than 84S. The stability of the 72S
ribosomes was less sensitive to pancreatic ribonuclease and low Mg-++
concentrations, dissociating below 0.1 mM Mg++. The 72S ribosomes were more
sensitive to elevated KCl concentrations, dissociation above 0.25 M.
Protein synthetic activity associated with the 72S class of ribosomes was
found in trypanosomes grown in rats. Under these conditions no cytochromes
or fully active Krebs cycle is present in these cells and respiration is
insensitive to cyanide.
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