• Journal of Applied Biological Chemistry
• /
• 제51권2호
• /
• pp.45-49
• /
• 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
• /
• 제34권2호
• /
• pp.113-119
• /
• 1991

저온 처리($4^{\circ}C$)가 벼(Oryza sativa L. cv. Samjin) 유식물 잎의 환원당, 설탕, 녹말 및 fructose-2,6-bisphosphate(F-2,$6-P_2$)의 함량에 미치는 영향을 조사하였으며, 이와 관련있는 amylase, invertase 및 fructose-1,6-bisphosphatase(FB-Pase)의 활성변화를 중심으로 3일 동안 측정하였다. 3일 동안 저온처리한 벼 유식물에서의 환원당과 설탕의 함량은 증가하였고, 수용성 녹말과 비수용성 녹말의 함량은 감소하였다. 한편, amylase의 활성은 증가하였고 acid invertase의 활성을 감소하였으며, alkaline invertase의 활성은 변화가 없었다. 스트로마 및 시토졸 FBPase의 활성은 감소하였다. 이에 부합되는 것으로 F-2,$6-P_2$의 함량이 감소하였다. 그러므로, 저온처리로 환원당의 함량이 증가한 것은 녹말 분해능의 증가에 기인한 것으로 사료되며, 설탕의 함량이 증가한 것은 설탕 분해능의 저하와 F-2,$6-P_2$의 함량감소에 따른 시토졸 FBPase의 활성증가에 기인한 것으로 해석된다. 또한 저온에 의한 이러한 탄수화물 대사의 변화는 벼 유식물의 저온 손상을 일부나마 방지하려는 기작이라 해석된다.

• Journal of Photoscience
• /
• 제4권3호
• /
• pp.141-145
• /
• 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.

• Journal of Plant Biotechnology
• /
• 제33권2호
• /
• pp.123-131
• /
• 2006

Chinese cabbage (Brassica rapa ssp. pekinesis) is one of the most important vegetable crops in korea and other East Asian countries. Cytosolic fructose-1,6-bisphospha-tase (cytFBPase) is a key enzyme in sucrose biosyn-thesis, which controls the sucrose levels as well as the productivity at plants. The Chinese cabbage cytFBPase gene, BrFBPase, encodes the 340 amino acid polypep-tide, giving a theoretical molecular weight of 37.2 kD and a isolectric point of 5.4. BrFBPase showed high sequence identity with Brassica homologs and its functional domains, such as 12,6P$_2$ binding site or active site and F6P binding site, were highly conserved in diverse sources of organisms. Although the genome of Chinese cabbage seemed to be triplicated, BrFBPase appears to be a single copy gene. The expression of BrFBPase was examined at transcript and protein levels under various conditions. BrFBPase expression was observed only in photosynthetic source tissue, not in sink tissue. The expression was slightly higher during the day than at night, and it showed a diurnal cycle with circadian rhythmicity. Short-term exposure to low temperature inhibited the expression of the BrFBPase, while long-term exposure increased the expression, supporting that sugar levels are high in late autumn when temperature are low.

• 한국식물생명공학회:학술대회논문집
• /
• 한국식물생명공학회 2005년도 추계학술대회 및 한일 식물생명공학 심포지엄
• /
• pp.9-21
• /
• 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.