PLANT PHYSIOLOGY , Vol 115, Issue 3 891-899, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Evidence for the Presence of a Porin in the Membrane of Glyoxysomes of Castor Bean
S. Reumann, M. Bettermann, R. Benz and H. W. Heldt
Institut fuer Biochemie der Pflanze, Universitaet Goettingen, Untere Karspuele 2. D-37073 Goettingen, Germany (S.R., M.B., H.W.H.)
Glyoxysomes of endosperm tissue of castor bean (Ricinus communis L.)
seedlings were solubilized in a detergent and added to a lipid bilayer.
Conductivity measurements revealed that the glyoxysomal preparation
contained a porin-like channel. Using an electrophysiological method, which
we established for semiquantitative determination of porin activity, we
were able to demonstrate that glyoxysomal membranes purified by sucrose
density gradient centrifugation contain an integral membrane protein with
porin activity. The porin of glyoxysomes was shown to have a relatively
small single-channel conductance of about 330 picosiemens in 1 M KCl and to
be strongly anion selective. Thus, the glyoxysomal porin differs from the
other previously characterized porins in the outer membrane of mitochondria
or plastids, but is similar to the porin of spinach (Spinacia oleracea L.)
leaf peroxisomes. Our results suggest that, in analogy to the porin of leaf
peroxisomes, the glyoxysomal porin facilitates the passage of small
metabolites, such as succinate, citrate, malate, and aspartate, through the
membrane.
