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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activities of certain enzymes related to the carbon assimilation pathway in whole leaves, mesophyll cell extracts, and bundle sheath extracts of the C(4) plant Panicum miliaceum have been measured and compared on a chlorophyll basis. Enzymes of the C(4) dicarboxylic acid pathway-phosphoenolpyruvate carboxylase and NADP-malic dehydrogenase-were localized in mesophyll cells. Carbonic anhydrase was also localized in mesophyll cell extracts. Ribose 5-phosphate isomerase, ribulose 5-phosphate kinase, and ribulose diphosphate carboxylase-enzymes of the reductive pentose phosphate pathway-were predominantly localized in bundle sheath extracts. High activities of aspartate and alanine transaminases and glyceraldehyde-3-P dehydrogenase were found about equally distributed between the photosynthetic cell types. P. miliaceum had low malic enzyme activity in both mesophyll and bundle sheath extracts.Isolated bundle sheath cells were capable of converting aspartate to oxalacetate at rates approaching the aspartate transaminase activity of bundle sheath extracts. The bundle sheath cells had a light induced CO(2) fixation of 23 mumoles of CO(2)/mg chl.hr in the absence of exogenous substrates.The photorespiratory enzymes, hydroxypyruvate reductase and glycolic oxidase, were about 3 fold higher in bundle sheath extracts than in mesophyll extracts when compared on a chlorophyll basis.
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PMID:Metabolic Activities in Extracts of Mesophyll and Bundle Sheath Cells of Panicum miliaceum (L.) in Relation to the C(4) Dicarboxylic Acid Pathway of Photosynthesis. 1665 52

Photosynthetically active bundle sheath strands capable of assimilating up to 8 micromoles CO(2) per milligram chlorophyll per hour have been isolated from fully expanded leaves of Zea mays L. Mesophyll cell contamination of the preparations was negligible, as evidenced by light and electron microscopy and by a high ratio of chlorophyll a to chlorophyll b in the strands. Ribose 5-phosphate markedly stimulated the rate of photosynthetic (14)CO(2) fixation by the isolated strands. In contrast, both pyruvate and phosphoenolpyruvate had a comparatively small stimulatory effect on bundle sheath (14)CO(2) fixation. After 5 minutes of photosynthesis in (14)C-bicarbonate, 95% of the incorporated (14)C was found in compounds other than C(4)-dicarboxylic acids, most notably in 3-phosphoglycerate and sugar phosphates. A similar distribution of (14)C was observed in the presence of exogenous ribose 5-phosphate. Extracts of bundle sheath strands contained high specific activities of "malic" enzyme, phosphoglycolate phosphatase, hydroxypyruvate reductase, and ribulose 1,5-diphosphate carboxylase, whereas the specific activities of NADP(+)-malate dehydrogenase and phosphopyruvate carboxylase were extremely low. These results indicate that the Calvin cycle occurs in the bundle sheath cells of maize.
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PMID:Photosynthetic carbon metabolism in isolated maize bundle sheath strands. 1665 10

Metabolomics coupled with heavy-atom isotope-labelled glucose has been used to probe the metabolic pathways active in cultured bloodstream form trypomastigotes of Trypanosoma brucei, a parasite responsible for human African trypanosomiasis. Glucose enters many branches of metabolism beyond glycolysis, which has been widely held to be the sole route of glucose metabolism. Whilst pyruvate is the major end-product of glucose catabolism, its transamination product, alanine, is also produced in significant quantities. The oxidative branch of the pentose phosphate pathway is operative, although the non-oxidative branch is not. Ribose 5-phosphate generated through this pathway distributes widely into nucleotide synthesis and other branches of metabolism. Acetate, derived from glucose, is found associated with a range of acetylated amino acids and, to a lesser extent, fatty acids; while labelled glycerol is found in many glycerophospholipids. Glucose also enters inositol and several sugar nucleotides that serve as precursors to macromolecule biosynthesis. Although a Krebs cycle is not operative, malate, fumarate and succinate, primarily labelled in three carbons, were present, indicating an origin from phosphoenolpyruvate via oxaloacetate. Interestingly, the enzyme responsible for conversion of phosphoenolpyruvate to oxaloacetate, phosphoenolpyruvate carboxykinase, was shown to be essential to the bloodstream form trypanosomes, as demonstrated by the lethal phenotype induced by RNAi-mediated downregulation of its expression. In addition, glucose derivatives enter pyrimidine biosynthesis via oxaloacetate as a precursor to aspartate and orotate.
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PMID:Probing the metabolic network in bloodstream-form Trypanosoma brucei using untargeted metabolomics with stable isotope labelled glucose. 2577 70