PASS Scripta Varia 21 - Pontifical Academy of Sciences

INTRACELLULAR PROTEIN DEGRADATION
Figure 3: APF-1/Ubiquitin is shifted to high molecular mass compound(s) following incubation
in ATP-containing crude cell extract. 125 I-labelled APF-1/ ubiquitin was incubated with reticulocyte
crude Fraction II in the absence (open circles) or presence (closed circles) of ATP, and the reaction
mixtures were resolved via gel filtration chromatography. Shown is the radioactivity measured in
each fraction. As can be seen, following addition of ATP, APF-1/ubiquitin becomes covalently attached
to some component(s) in fraction II, which could be another enzyme of the system or its
substrate(s) (with permission from Proceedings of the National Academy of the USA; published
originally in Ref. 39).
these organisms (unpublished) showed that ubiquitin is restricted only to eukaryotes.
The finding of ubiquitin in bacteria (44) was probably due to contamination
of the bacterial extract with yeast ubiquitin derived from the yeast
extract in which the bacteria were grown. While in retrospect the name ubiquitin
is a misnomer, as it is restricted to eukaryotes and is not ubiquitous as
was previously thought, for historical reasons it has still remained the name of
the protein. Accordingly, and in order to avoid confusion, I suggest that the
names of other novel enzymes and components of the ubiquitin system, but
of other systems as well, should remain as were first coined by their discoverers.
The Scientific Legacy of the 20 th Century
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