Lysine Catabolism in Barley (<i>Hordeum vulgare</i> L.)

Møller, Birger Lindberg

doi:10.1104/pp.57.5.687

Cited by 19 publications

(10 citation statements)

References 27 publications

(33 reference statements)

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“…The (4,5,19), no LKR activity was detected either in control plants or in transgenic plants expressing the bacterial DHPS constitutively (data not shown). (iii) Feeding of radioactive lysine into cereal grains has shown that lysine is efficiently catabolized in this organ via saccharopine into a-aminoadipic acid and glutamate (8)(9)(10). This conclusion was supported by the demonstration that developing cereal grains also exhibited relatively high activity of the enzyme LKR, which converts lysine into saccharopine (7).…”

Section: Seedsupporting

confidence: 64%

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Lysine synthesis and catabolism are coordinately regulated during tobacco seed development.

Karchi

Shaul

Galili

1994

Proc. Natl. Acad. Sci. U.S.A.

123

106

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The regulation of synthesis and accumulation of the essential amino acid lysine was studied in seeds of transgenic tobacco plants expressing, in a seed-specific manner, two feedback-insensitive bacterial enzymes: dihydrodipicolinate synthase (EC 4.2.1.52) and aspartate kinase (EC 2.7.2.4). High-level expression of the two bacterial enzymes resulted in only a slight increase in free lysine accumulation at intermediate stages of seed development, while free lysine declined to the low level of control plants toward maturity. To test whether enhanced catabolism may have contributed to the failure offree lysine to accumulate in seeds oftransgenic plants, we analyzed the activity of lysine-ketoglutarate reductase (EC 1.5.1.7), an enzyme that catabolizes lysine into saccharopine. In both the control and the transgenic plants, the timing of appearance of lysine-ketoglutarate reductase activity correiated very closely with that of dihydrodipicolinate synthase activity, suggesting that lysine synthesis and catabolism were coordinately regulated during seed development. Notably, the activity of lysine-ketoglutarate reductase was significantly higher in seeds of the transgenic plants than in the controls. Coexpression of both bacterial enzymes in the same plant resulted in a significant increase in the proportions oflysine and threonine in seed albumins. Apparently, the normal low steady-state levels of free lysine and threonine in tobacco seeds may be rate limiting for the synthesis of seed proteins, which are relatively rich in these amino acids.Like many bacterial species, higher plants synthesize the essential amino acid lysine from aspartate by a specific branch of the aspartate-family pathway (1, 2). Biochemical studies demonstrated that lysine feedback inhibits the activities of two key enzymes in its pathway; aspartate kinase (AK) and dihydrodipicolinate synthase (DHPS) (1,2). Yet, analyses of mutant and transgenic plants, carrying enzymes with reduced sensitivity to feedback inhibition, showed that lysine synthesis is regulated primarily by .The regulation of synthesis and accumulation of lysine in seeds is poorly understood. Plant seeds generally contain low levels of free threonine and only trace amounts of free lysine (6). In addition, these amino acids are present in very low amounts in many seed proteins (6). Previous studies suggested that free lysine may be catabolized rather efficiently in developing plant seeds (7-10). Yet the role of such processes in the accumulation of lysine in seeds has not been elucidated.To study the regulation of lysine synthesis and accumulation in plant seeds, we have expressed a chimeric gene encoding a bacterial DHPS, either by itself or together with another chimeric gene encoding a bacterial insensitive AK (11), in a seed-specific manner in transgenic tobacco plants. Although this expression resulted in increased lysine synthesis during seed development, free lysine failed to accumulate to high level in mature seeds. Notably, the transient increase of free lysine in t...

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Section: Seedsupporting

confidence: 64%

“…In addition, these amino acids are present in very low amounts in many seed proteins (6). Previous studies suggested that free lysine may be catabolized rather efficiently in developing plant seeds (7)(8)(9)(10). Yet the role of such processes in the accumulation of lysine in seeds has not been elucidated.…”

mentioning

confidence: 97%

Lysine synthesis and catabolism are coordinately regulated during tobacco seed development.

Karchi

Shaul

Galili

1994

Proc. Natl. Acad. Sci. U.S.A.

123

106

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“…The sections of the gel in the region of the purified LKR/SDH bands are illustrated below each peak, and the bands are indicated by arrows on the right. ledonous plant species (Moeller, 1976;BrochettoBraga et al, 1992;Gaziola et al, 1997).…”

Section: Biochemical Properties Of Soybean Lkr and Sdhmentioning

confidence: 99%

“…In both types of organisms, excess Lys is catabolized via the ␣-amino adipic acid pathway, also named as the saccharopine pathway (Moeller, 1976;Arruda et al, 1982;Arruda and Da Silva, 1983;Markovitz et al, 1984;Brochetto-Braga et al, 1992;Galili, 1995;Goncalves-Butruille et al, 1996;Azevedo et al, 1997). The first enzyme in the Lys catabolic pathway is Lys-ketoglutarate reductase (LKR), also named as Lys 2-oxoglutarate reductase, which condenses Lys and ␣-ketoglutarate into saccharopine and uses the co-factor NADPH.…”

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confidence: 99%

Purification and Characterization of Bifunctional Lysine-Ketoglutarate Reductase/Saccharopine Dehydrogenase from Developing Soybean Seeds

et al. 2000

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Both in mammals and plants, excess lysine (Lys) is catabolized via saccharopine into ␣-amino adipic semialdehyde and glutamate by two consecutive enzymes, Lys-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH), which are linked on a single bifunctional polypeptide. To study the control of metabolite flux via this bifunctional enzyme, we have purified it from developing soybean (Glycine max) seeds. LKR activity of the bifunctional LKR/SDH possessed relatively high K m for its substrates, Lys and ␣-ketoglutarate, suggesting that this activity may serve as a rate-limiting step in Lys catabolism. Despite their linkage, the LKR and SDH enzymes possessed significantly different pH optima, suggesting that SDH activity of the bifunctional enzyme may also be rate-limiting in vivo. We have previously shown that Arabidopsis plants contain both a bifunctional LKR/SDH and a monofunctional SDH enzymes (G. Tang, D. Miron, J.X. Zhu-Shimoni, G. Galili [1997] Plant Cell 9: 1-13). In the present study, we found no evidence for the presence of such a monofunctional SDH enzyme in soybean seeds. These results may provide a plausible regulatory explanation as to why various plant species accumulate different catabolic products of Lys.

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“…Most of the available data were obtained in studies on the incorporation and metabolism of radiolabeled precursors by plant tissues. Feeding experiments with ["4C]lysine demonstrated the incorporation of radioactivity into a-amino adipic acid and glutamic acid in wheat (18) and into saccharopine and diaminopimelic acid in maize and barley (16,26). In developing endosperm of maize and barley, radiolabeled lysine is incorporated primarily into glutamic acid and proline (4, 26).…”

mentioning

confidence: 99%

Partial Purification and Characterization of Lysine-Ketoglutarate Reductase in Normal and Opaque-2 Maize Endosperms

Brochetto-Braga¹,

Leite²,

Arruda³

1992

Plant Physiol.

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Lysine-ketoglutarate reductase catalyzes the first step of lysine catabolism in maize (Zea mays L.) endosperm. The enzyme condenses L-lysine and a-ketoglutarate into saccharopine using NADPH as cofactor. It is endosperm-specific and has a temporal pattern of activity, increasing with the onset of kernel development, reaching a peak 20 to 25 days after pollination, and thereafter decreasing as the kernel approaches maturity. The enzyme was extracted from the developing maize endosperm and partially purified by ammonium-sulfate precipitation, anion-exchange chromatography on DEAE-cellulose, and affinity chromatography on Blue-Sepharose CL-6B. The preparation obtained from affinity chromatography was enriched 275-fold and had a specific activity of 411 by the opaque-2 mutation may explain, at least in part, the elevated concentration of lysine found in the opaque-2 endosperm.There is little information on lysine catabolism in higher plants. Most of the available data were obtained in studies on the incorporation and metabolism of radiolabeled precursors by plant tissues. Feeding experiments with ["4C]lysine demonstrated the incorporation of radioactivity into a-amino adipic acid and glutamic acid in wheat (18) and into saccharopine and diaminopimelic acid in maize and barley (16,26). In developing endosperm of maize and barley, radiolabeled lysine is incorporated primarily into glutamic acid and proline (4, 26). These findings indicate that lysine is catabolized in plants via the saccharopine pathway.The first enzymatic evidence for the operation of the saccharopine pathway for lysine catabolism in plants was obtained with the demonstration of LKR3 activity in immature endosperm of maize (3). LKR (EC 1.5.1.8) condenses lysine and a-ketoglutarate into saccharopine using NADPH as cofactor.An understanding of the pathways for lysine biosynthesis and degradation in plants has enormous importance because of the limiting concentration of this essential amino acid in major food sources such as cereals. Valuable information can be obtained by the elucidation of the properties of enzymes involved in the biosynthesis and catabolism of lysine and by the use of mutants in which the activities of the enzymes are altered.Since the discovery of the superior nutritive value of the high lysine maize mutant opaque-2 (15), there have been many studies on the effects of this mutant gene on protein and amino acid metabolism in maize endosperm. The opaque-2 gene is located on the short arm of chromosome 7 and its major effect is the reduction of the maize storage protein zein. This is a complex of polypeptides coded by a multigenic family located on chromosomes 4 and 7 (23). The opaque-2 gene in the homozygous form reduces the zein content of the endosperm by up to 70% (6). The reduction is

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Lysine Catabolism in Barley (Hordeum vulgare L.)

Cited by 19 publications

References 27 publications

Lysine synthesis and catabolism are coordinately regulated during tobacco seed development.

Lysine synthesis and catabolism are coordinately regulated during tobacco seed development.

Purification and Characterization of Bifunctional Lysine-Ketoglutarate Reductase/Saccharopine Dehydrogenase from Developing Soybean Seeds

Partial Purification and Characterization of Lysine-Ketoglutarate Reductase in Normal and Opaque-2 Maize Endosperms

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