In reply to Krystina Rybicka's posting:
There are several reasons that can be put forward to apply the name
glycosome to the trypanosomatid microbodies rather than to the
glycogen-protein particles of animal cells.
First, there are some important objections to the use of the privileged
suffix -some in the case of an enzyme particle, or an enzyme cluster
belonging to a metabolic pathway. By now there is ample evidence in the
literature of metabolite channelling as the result of interactions between
macromolecules, leading to the formation of pathway particles. Actually
some researchers consider the cytosol to represent one big aggregate of
macromolecules. If they all would receive the suffix -some the entire cell
would be loaded with "somes". Therefore, it is my opinion that the suffix
-some should represent something more than just a particle. We (Piet Borst
and myself) have chosen the name glycosome to indicate that we deal with a
true
membrane-bounded organelle, as shown by its morphology, its sedimentation
behaviour, its equilibrium density in sucrose and percoll gradients and the
fact that all enzymes exhibit a high degree of latency. Moreover, the
glycosome constitutes a compartment of glycolytic intermediates, which is
clearly separated from the cytosol in intact cells, as has been shown by
pulse-labelling experiments. Moreover, there is sufficient historical
precedence to reserve the suffix -some for membrane-bounded organelles
(e.g. lysosomes, peroxisomes, glyoxysomes, hydrogenosomes, microsomes). For
a true pathway particle, enzyme aggregate, or enzyme cluster, the term
particle or complex is preferred.
Second, Krystina Rybicka states that the name glycosome for glycogen-protein
particles was already proposed in 1968 by Scott and Still. This is only
partly true. Throughout the entire paper Scott and Still use the term
particle to describe the behaviour of glycogen particles. Nowhere do they
show the association of their glycogen particles with proteins. The name
"glycosome" appears only in the very last sentence of their paper and the
proposal for such a name is not based on any experimental fact. Moreover,
if they would have meant to propose the name of a new organelle, they
would have done so in a more conspicuous place.
Third, The fact that there was no solid experimental basis to propose such
a name as the "glycosome" for glycogen particles, must have been the reason
why this name never became accepted in the glycogen world. It took 9 years
before Rybicka used the name again. It was then used occasionally between
1977 till 1981, in not more than a few papers.
Fourth, In 1977 Opperdoes and Borst published their paper on the
trypanosomid glycosome. Rybicka made mention of this fact in her Virchows
Archiv's paper in 1979. At that time the debate on the appropriate or
inappropriate use of the name glycosome for either organelle should have
started. Instead between 1981 and the 1996 not a single original
publication on "glycosomes" of glycogen has appeared in the literature,
except the recent review paper by Krystina Rybicka that has provoked this
discussion.
Finally, contrary to "glycosomes" of glycogen, the glycosomes of the
Trypanosomatidae are widely accepted. Since 1977 at least 111 papers with
the name glycosome in the title and all referring to the trypanosomatid
organelle have been published in the international and refereed literature.
Glycosomes are being discussed widely in parasitology text books, in review
papers and in textbooks on peroxisomes and cell organelles where they are
put at the same level as peroxisomes.
My conclusion, therefore, is that there is no reason whatsoever to change
the name of the trypanosomatid glycosome. If the use of the name glycosome
for trypanosomes would have caused confusion amongst glycogen biochemist
and cell biologist, its name would have been changed already 19 years ago,
simply by mass action.
Fred Opperdoes
