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glyoxylate cycle in Chlamy (summary)

P. Zheng pzheng at BLUE.WEEG.UIOWA.EDU
Mon Feb 19 23:38:50 EST 1996

=09I would like to thank everyone that responded to the question=20
regarding the location of Chlamydomonas glyoxylate cycle that I raised on=
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
=09A.  By cellular fractionation, it was shown that the marker=20
enzyme of glyoxylate cycle, isocitrate lyase (ICL) was not located in the=
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(GenBank accession #U18765, submitted by S. Petridou,unpublished).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=
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.

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