Arginine degradation by arginase in mitochondria of soybean seedling cotyledons |
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Authors: | Ariel Goldraij Joe C Polacco |
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Institution: | (1) Department of Biochemistry and Interdisciplinary Plant Group, 117 Schweitzer Hall, University of Missouri, Columbia, Missouri 65211, USA, US |
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Abstract: | Arginase (EC 3.5.3.1) localization was studied in soybean (Glycine max L.) seedling cotyledons. Subcellular fractionation in a discontinuous Percoll gradient showed that arginase was localized
in the mitochondrion. Arginine (Arg) uptake by mitochondria was demonstrated by co-sedimentation of 3H]Arg-derived label and the mitochondrial marker enzyme cytochrome c oxidase. Arginine uptake was complete in about 10 min. Since detergent but not NaCl released most label, we conclude that
Arg was taken up and not bound to the organellar surface. Arginine transport was not saturable, at least up to 20 mM. Basic
amino acids were the best inhibitors of Arg uptake. The uncoupler 2,4-dinitrophenol did not inhibit Arg uptake. At least 30%
of l-guanido-14C]Arg taken up by mitochondria was degraded by arginase in seedling cotyledons, while little or no degradation was detected
in mitochondria from developing embryos, even though the Arg uptake level was similar in both mitochondrial preparations.
These results are consistent with our previously reported pattern of arginase expression and urea accumulation during embryo
development and seed germination (A. Goldraij and J.C. Polacco, 1999, Plant Physiol. 119: 297–303). The lack of Arg degradation
allows developing embryos to conserve Arg, the main N-reserve amino acid utilized by germinating soybean.
Received: 7 July 1999 / Accepted: 21 September 1999 |
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Keywords: | : Arginine (uptake degradation) – Arginase (location activity) – Glycine (N reserve) – Mitochondrion |
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