• Journal of Applied Biological Chemistry
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• v.51 no.2
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• pp.45-49
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• 2008

Cytosolic fructose-1,6-bisphosphatase (cFBPase) in plants is a key regulatory enzyme in the photosynthetic sucrose biosynthesis. Plant cFBPases, like the mammalian FBPases, are inhibited by adenosine 5'-monophosphate (AMP) and fructose-2,6-bisphosphate (Fru-2,6-$P_2$). In the mammalian FBPases, Lys112 and Tyr113 play important roles in the AMP binding. To understand roles of the corresponding residues, Lys115 and Tyr116, in pea cFBPase, the mutant cFBPases were generated by site-directed mutagenesis. The alterations of Lys115 to Gin and Tyr116 to Phe displayed small changes in $K_m$ and $K_i$ for Fru-2,6-$P_2$, indicating that the mutation causes minor effects on the enzyme catalysis and Fru-2,6-$P_2$ binding, whereas resulted in higher than 500-fold increase of $[AMP]_{0.5}$ compared with that of the wild-type enzyme. Results indicate the residues Lys115 and Tyr116 play important roles in the binding of AMP to the allosteric site of the pea cFBPase.

• Journal of Plant Biology
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• v.34 no.2
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• pp.113-119
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• 1991

The contents of reducing sugar, sucrose, starch and fructose-2,6-bisphosphate (F-Z,$6-P_2$) in relation to the activities of amylase, invertase and fructose-1,6-bisphosphatase (FBPase) were investigated from the leaves of rice (Oryza sativa L. cv. Samjin) seedlings grown at $4^{\circ}C$ for 3 days_ In the seedlings, the contents of reducing sugar and sucrose were increased, but soluble and insoluble starch were declined. Under this condition, amylase activity was increased. but acid invertase activity was declined and alkaline invertase activity was not changed. Cytosolic and stromal FBPase activities were increased. But F-2,$6-P_2$ content was declined. It seemed that the increase of reducing sugar content might be due to the increased activity of amylase and the increase of sucrose content might be related to the increased activity of cytosolic FBPase, reduced content of F-Z,$6-P_2$ and reduced rate of hydrolysis of sucrose during the cold treatment. These results suggested that the changes in carbohydrate rnetabolim of rice seedlings under low temperature reflect one of the protection mechanism to the low temperature during the cold treatment.atment.

• Journal of Photoscience
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• v.4 no.3
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• pp.141-145
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• 1997

Polymerase chain reaction(PCR) was conducted with a pea cDNA library using two primers synthesized from homology analysis of amino acid sequences for animal and plant cytosolic FBPases. A PCR product with 650 bp long was cloned into pGEM-T vector and sequenced. The deduced amino acid sequence of the cDNA fragment was 98, 91, and 85% homologous with those of cytosolic FBPases from spinach, sugarbeet, and sugarcane, respectively. It was 51% homologous with amino acid sequence of FBPase from pea chloroplasts. Northern blot analysis was proceeded with the cDNA clone resulting that 1.2 kb transcript was highly expressed in light-grown pea leaves but almost not expressed in dark-grown etiolated pea seedlings. When peas grown in the light for 10 days were transferred to darkness, the transcript was gradually decreased with dark treatment, indicating that the expression of the enzyme was induced by continuous white light but suppressed by dark treatment. Pea cytosolic FBPase was highly expressed in leaves with trace amounts in stems. but almost not expressed in roots.

• Proceedings of the Korean Society of Plant Biotechnology Conference
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• 2005.11a
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• pp.9-21
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• 2005

To study the biochemical and physiological role of the plastidic glucose transporter (pGlcT) in carbohydrate metabolism, we characterized transgenic plants with mutations in the pGlcT gene (GT), gt-1 and gt-2, as well double mutants of GT and the maltose transporter (MEX1) and GT and the triose phosphate/phosphate translocator (TPT), GT and the cytosolic fructose-1,6-bisphosphatase gene (cFBP), and MEX1 and TPT, gt-1/mex2, gt-1/tpt-2, gt-1/cfbp-1, mex1-1/tpt-2, respectively. Compared to the wild type, all mutants except the gt-1/cfbp-1 mutant lines displayed higher starch accumulation and higher levels of maltose. Starch accumulation is due to a decrease in starch turnover, leading to an imbalance between the rates of synthesis and degradation. Sucrose levels of gt alleles were higher than those in wild-type plants during the light period, suggesting possible nightly supplementation via the maltose transport pathway to maintain proper carbohydrate partitioning in the plant leaves. The gt plants displayed less growth retardation than mex1-1 mutant and gt-1/mex2 double mutant displayed accumulativesevere growth retardation as compared to individual gt-1 and mex1-1 mutants, implying that the maltose transporter-mediated pathway is a major route for carbohydrate partitioning at night. The gt-1/tpt-2, mex1-1/tpt-2 and gt-1/cfbp-1 double mutants had retarded growth and low chlorophyll content to differing degrees, indicating that photosynthetic capacity had diminished. Interestingly, the gt-1/tpt-2 line displayed a glucose-insensitive phenotype and higher germination rates than wild type, suggesting its involvement not only in carbon partitioning, but also in the sugar signaling network of the pGlcT and TPT.