Triose phosphate translocator (TPT) is located in the inner membrane of plant chloroplasts. It catalyzes the counter exchange of those phosphate/3-phosphoglycerate and phosphate. To obtain the basic information on the...Triose phosphate translocator (TPT) is located in the inner membrane of plant chloroplasts. It catalyzes the counter exchange of those phosphate/3-phosphoglycerate and phosphate. To obtain the basic information on the structure-function relation, a cDNA encoding the complete precursor of the triose phosphate translocator has been isolated from wheat (Triticum aestivum L.) by RACE ( rapid amplification of cDNA ends) strategies. The wheat TPT cDNA encodes a precursor protein of 402 amino acid residues with a deduced molecular weight of 43 kD. A putative processing site between Ala-78 and Ala-79 of the precursor protein is suggested by comparison with those of the TPTs from spinach (Spinacia oleracea Mill.) and maize (Zea mays L.). The mature part of wheat TPT consists of 324 amino acid with a molecular weight of 35 kD, which share 89% identity with maize TPT. The amino acids Lys-274 and Arg-275 (mature protein) which is regarded as the substrate-binding site, are both conserved in plant TPTs. The gene expression analysis for leaves, coleoptiles, roots and seeds of wheat showed that the TPT transcript was only detectable in leaves and coleoptiles. No apparent expression signal was detected in the roots and seeds. This indicated that the expression of wheat TPT might be restricted to green tissues.展开更多
In plants, triose phosphate/phosphate translocator (TPT) is the first regulation point forpartitioning of photosynthate between source and sink. Studies on the characteristic of TPT and itsregulation on the distributi...In plants, triose phosphate/phosphate translocator (TPT) is the first regulation point forpartitioning of photosynthate between source and sink. Studies on the characteristic of TPT and itsregulation on the distribution of assimilates are critical for improving the utilization rate of photosyntheticassimilates. Chloroplasts with intactness of more than 91% and high purity were isolated from wheat( Triticurn aestivurn L. cv. Jing 411) leaves. Analysis of SDS-PAGE and labeling with an irreversible specificinhibitor, [H3]2^-DIDS (4, 4'-diisothiocyano-2, 2'-stilbenedisulfonate, DIDS) demonstrated that wheat TPTwas a chloroplast membrane protein with a 35 kD molecular weight, which comprised about 15% of the totalmembrane proteins of chloroplasts. Western blotting analysis showed that wheat TPT is uniquelydistributed in the envelope membrane of chloroplasts, but not detected in the membranes of vacuoles andmitochondria. The silicone-oil-layer centrifugation system was employed to study the kinetic properties ofTPT. The results showed that the maximal transport activity of TPT was the highest for dihydroxyacetonephosphate (DHAP)/inorganic phosphate (Pi), then for phosphoenolpyruvate (PEP)/Pi and glucose-6-phosphate (G6P)/Pi. The Km value of TPT was the lowest for DHAP, followed by Pi, PEP and G6P,therefore the most preferred substrate of TPT is DHAP. The transport of wheat TPT to DHAP was stronglyinhibited by DIDS with a degree of 95%. Inhibition of TPT transport activity led to an obvious accumulationof starch in chloroplasts, therefore the TPT protein of wheat controls the export of TP out of chloroplastsinto cytosol. Except for the need of participating in the Calvin cycle, the ratio of TP exported out ofchloroplast to the one used for synthesizing starch was at least 93.6:6.4. The TPT protein from wheat hasmuch high transport efficiency, which plays an important role in the regulation of the distribution ofassimilates in wheat chloroplasts.展开更多
文摘Triose phosphate translocator (TPT) is located in the inner membrane of plant chloroplasts. It catalyzes the counter exchange of those phosphate/3-phosphoglycerate and phosphate. To obtain the basic information on the structure-function relation, a cDNA encoding the complete precursor of the triose phosphate translocator has been isolated from wheat (Triticum aestivum L.) by RACE ( rapid amplification of cDNA ends) strategies. The wheat TPT cDNA encodes a precursor protein of 402 amino acid residues with a deduced molecular weight of 43 kD. A putative processing site between Ala-78 and Ala-79 of the precursor protein is suggested by comparison with those of the TPTs from spinach (Spinacia oleracea Mill.) and maize (Zea mays L.). The mature part of wheat TPT consists of 324 amino acid with a molecular weight of 35 kD, which share 89% identity with maize TPT. The amino acids Lys-274 and Arg-275 (mature protein) which is regarded as the substrate-binding site, are both conserved in plant TPTs. The gene expression analysis for leaves, coleoptiles, roots and seeds of wheat showed that the TPT transcript was only detectable in leaves and coleoptiles. No apparent expression signal was detected in the roots and seeds. This indicated that the expression of wheat TPT might be restricted to green tissues.
文摘In plants, triose phosphate/phosphate translocator (TPT) is the first regulation point forpartitioning of photosynthate between source and sink. Studies on the characteristic of TPT and itsregulation on the distribution of assimilates are critical for improving the utilization rate of photosyntheticassimilates. Chloroplasts with intactness of more than 91% and high purity were isolated from wheat( Triticurn aestivurn L. cv. Jing 411) leaves. Analysis of SDS-PAGE and labeling with an irreversible specificinhibitor, [H3]2^-DIDS (4, 4'-diisothiocyano-2, 2'-stilbenedisulfonate, DIDS) demonstrated that wheat TPTwas a chloroplast membrane protein with a 35 kD molecular weight, which comprised about 15% of the totalmembrane proteins of chloroplasts. Western blotting analysis showed that wheat TPT is uniquelydistributed in the envelope membrane of chloroplasts, but not detected in the membranes of vacuoles andmitochondria. The silicone-oil-layer centrifugation system was employed to study the kinetic properties ofTPT. The results showed that the maximal transport activity of TPT was the highest for dihydroxyacetonephosphate (DHAP)/inorganic phosphate (Pi), then for phosphoenolpyruvate (PEP)/Pi and glucose-6-phosphate (G6P)/Pi. The Km value of TPT was the lowest for DHAP, followed by Pi, PEP and G6P,therefore the most preferred substrate of TPT is DHAP. The transport of wheat TPT to DHAP was stronglyinhibited by DIDS with a degree of 95%. Inhibition of TPT transport activity led to an obvious accumulationof starch in chloroplasts, therefore the TPT protein of wheat controls the export of TP out of chloroplastsinto cytosol. Except for the need of participating in the Calvin cycle, the ratio of TP exported out ofchloroplast to the one used for synthesizing starch was at least 93.6:6.4. The TPT protein from wheat hasmuch high transport efficiency, which plays an important role in the regulation of the distribution ofassimilates in wheat chloroplasts.
