=09I would like to thank everyone that responded to the question=20
regarding the location of Chlamydomonas glyoxylate cycle that I raised on=
=20
the Chlamy at net.bio.net on Jan 27, 1996.
=09I believe that the Glyoxylate cycle in Chlamydomonas is probably=20
indeed located in the cytosol based on the following:=20
=09
=09A. By cellular fractionation, it was shown that the marker=20
enzyme of glyoxylate cycle, isocitrate lyase (ICL) was not located in the=
=20
microbodies or any other organelles but in the cytosol in unicellular=20
green algae such as Chlorogonium (Stabenau, 1984) and Eremosphaera=20
(Stabenau, 1974). Stabenau further concluded that the microbodies in=20
these organisms were unspecialized and the entire glyoxylate cycle was=20
located in the cytosol. =20
=09B. I don=D5t know whether anybody has ever isolated microbodies=20
from Chlamydomonas and assayed for ICL activities. However, a full=20
length cDNA encoding Chlamydomonas reinhardtii ICL has been cloned=20
(GenBank accession #U18765, submitted by S. Petridou,unpublished). I=20
aligned the deduced amino acid sequence of Chlamydomonas ICL with other=20
known ICLs and found that Chlamy ICL (416 AA) is very similar to=20
other bacterial ICLs in terms of length (429-434 AA) and amino acid=20
compositions (55 to 57% identities) but different from other eukaryotic=20
ICLs (536 to 576 AA, 26 to 36% identities with Chlamy ICL). Furthermore=20
there are no major gaps between chlamy ICL and bacterial ICLs except a 10=
=20
to 12-AA segment (position 10 to 22 from the N-terminus) that is missing=20
in Chlamy ICL. These data suggest that Chlamy ICL probably does not=20
contain signals for organelle import and is a cytosolic enzyme just like=20
other unicellular green algal ICLs (no otherunicellular green algal ICL=20
sequences have been cloned). Therefore, the glyoxylate cycle in Chlamy=20
is also located in the cytosol.
