Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.1.18 (branching enzyme)
 628 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The localization of enzymes involved in the flow of carbon into and out of starch was determined in guard cells of Commelina communis. The guard cell chloroplasts were separated from the rest of the cellular components by a modification of published microfuge methods. The enzymes of interest were then assayed in the supernatant and chloroplast fractions. The chloroplast yield averaged 75% with 10% cytoplasmic contamination. The enzymes involved in starch biosynthesis, ADPglucose pyrophosphorylase, starch synthase, and branching enzyme, are located exclusively in the chloroplast fraction. The enzymes involved in starch degradation show a more complex distribution. Phosphorylase is located in both the supernatant and chloroplast fraction, 50% in each fraction. Most of the amylase and debranching enzyme activity is present in the supernatant (70%) fraction. The majority of the rest of the enzymes involved in the degradation of starch to malate and synthesis of starch from a hexose precursor were also investigated. All of the enzymes were present in the chloroplast except for hexokinase and phosphofructokinase. The inability to assay these enzymes could possibly have been due to the lack of or low activity of the enzymes or to nonoptimal assay conditions.
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PMID:Localization of Carbohydrate Metabolizing Enzymes in Guard Cells of Commelina communis. 1666 2

Activities of the enzymes of gluconeogenesis and of starch metabolism were measured in extracts of amyloplasts isolated from protoplasts derived from 14-day-old maize (Zea mays L., cv Pioneer 3780) endosperm. The enzymes triosephosphate isomerase, fructose-1,6-bisphosphate aldolase, fructose-1,6-bisphosphatase, phosphohexose isomerase, phosphoglucomutase, ADPG pyrophosphorylase, UDPG pyrophosphorylase, soluble and bound starch synthases, and branching enzyme were found to be present in the amyloplasts. Of the above enzymes, ADPG pyrophosphorylase had the lowest activity per amyloplast. Invertase, sucrose synthase and hexokinase were not detected in similar amyloplast preparations. Only a trace of the cytoplasmic marker enzyme alcohol dehydrogenase could be detected in purified amyloplast fractions. In separate experiments, purified amyloplasts were lysed and then supplied with radioactively labeled glucose-6-phosphate, glucose-1-phosphate, fructose-1,6-bisphosphate, dihydroxyacetone phosphate, glucose, fructose, sucrose, and 3-0-methylglucose in the presence of adenosine triphosphate or uridine triphosphate. Of the above, only the phosphorylated substrates were incorporated into starch. Incorporation into starch was higher with added uridine triphosphate than with adenosine triphosphate. Dihydroxyacetone phosphate was the preferred substrate for uptake by intact amyloplasts and incorporation into starch. In preliminary experiments, it appeared that glucose-6-P and fructose-1,6-bisphosphate may also be taken up by intact amyloplasts. However, the rate of uptake and incorporation into starch was relatively low and variable. Additional study is needed to determine conclusively whether hexose phosphates will cross intact amyloplast membranes. From these data, we conclude that: (a) Triose phosphate is the preferred substrate for uptake by intact amyloplasts. (b) Amyloplasts contain all enzymes necessary to convert triose phosphates into starch. (c) Sucrose breakdown must occur in the cytosol prior to carbohydrate transfer into the amyloplasts. (d) Under the conditions of assay, amyloplasts are unable to convert glucose or fructose to starch. (e) Uridine triphosphate may be the preferred nucleotide for conversion of hexose phosphates to starch at this stage of kernel development.
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PMID:Enzyme activities associated with maize kernel amyloplasts. 1666 89

Starch branching enzyme (SBE) activity in the cassava storage root exhibited a diurnal fluctuation, dictated by a transcriptional oscillation of the corresponding SBE genes. The peak of SBE activity coincided with the onset of sucrose accumulation in the storage, and we conclude that the oscillatory mechanism keeps the starch synthetic apparatus in the storage root sink in tune with the flux of sucrose from the photosynthetic source. When storage roots were uncoupled from the source, SBE expression could be effectively induced by exogenous sucrose. Turanose, a sucrose isomer that cannot be metabolized by plants, mimicked the effect of sucrose, demonstrating that downstream metabolism of sucrose was not necessary for signal transmission. Also glucose and glucose-1-P induced SBE expression. Interestingly, induction by sucrose, turanose and glucose but not glucose-1-P sustained an overt semidian (12-h) oscillation in SBE expression and was sensitive to the hexokinase (HXK) inhibitor glucosamine. These results suggest a pivotal regulatory role for HXK during starch synthesis. Abscisic acid (ABA) was another potent inducer of SBE expression. Induction by ABA was similar to that of glucose-1-P in that it bypassed the semidian oscillator. Both the sugar and ABA signaling cascades were disrupted by okadaic acid, a protein phosphatase inhibitor. Based on these findings, we propose a model for sugar signaling in regulation of starch synthesis in the cassava storage root.
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PMID:Sugar-mediated semidian oscillation of gene expression in the cassava storage root regulates starch synthesis. 1951 34

In plants, starch is synthesized in leaves during the day-time from fixed carbon through photosynthesis and is mobilized at night to support continued respiration, sucrose export, and growth in the dark. The main crops where starch is biosynthesized and stored are corn, rice, wheat, and potatoes, and they are mainly used as food resources for humankind. There are many genes that are involved in starch biosynthesis from cytosol to storage organs in plants. ADP-glucose, UDP- glucose, and glucose-6-phosphate are synthesized catalyzed by UDP-invertase, AGPase, hexokinase, and P- hexose-isomerase in cytosol. Starch composed of amylopectin and amylose is synthesized by starch synthase, granule bound starch synthase, starch-branching enzyme, debranching enzyme, and pullulanase, which is primarily responsible for starch production in storage organs. Recently, it has been uncovered that structural genes are controlled by proteins derived from other genes such as transcription factors. To obtain more precise information on starch metabolism, the functions of genes and transcription factors need to be studied to understand their roles and functions in starch biosynthesis in plants. However, the roles of genes related to starch biosynthesis are not yet clearly understood. The papers of this special issue contain reviews and research articles on these topics and will be a useful resource for researchers involved in the quality improvement of starch storage crops.
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PMID:Functional Analysis of Starch Metabolism in Plants. 3289 39