Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.1.1 (hexokinase)
 5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The aim of this work was to discover the pathway of starch breakdown in the photosynthetic tissues of Pisum sativum. 2. Measurements of the starch in the leaves of plants grown in photoperiods of 12 or 18 h showed that starch, synthesized in the light, was rapidly metabolized in the dark at rates of 0.04--0.06 mumol glucose/min per g fresh weight. 3. The maximum catalytic activities of alpha-amylase, beta-amylase, hexokinase, alpha-glucan phosphorylase and phosphoglucomutase in extracts of leaves showed no diurnal variation in either photoperiod, and exceeded estimates of the rate of net starch breakdown in the dark. 4. Studies with intact chloroplasts, isolated from young shoots and from leaves, indicated that pea chloroplasts do not contain significant activities of alpha-amylase, beta-amylase and hexokinase, although some of the latter may be attached to the outside of the chloroplast envelope. These studies also showed that pea chloroplasts contained sufficient alpha-glucan phosphorylase and phosphoglucomutase to mediate the observed rates of starch breakdown. 5. It is proposed that starch breakdown in pea chloroplasts is phosphorolytic.
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PMID:Pathway of starch breakdown in photosynthetic tissues of Pisum sativum. 15 56

Expression of genes coding for sporamin and beta-amylase, the two most abundant proteins in storage roots of sweet potato, is coordinately inducible in atypical vegetative tissues by sugars. A sweet potato gene for beta-amylase (beta-Amy) with introns as well as a beta-Amy::GUS fusion gene composed of the beta-Amy promoter and the GUS coding sequence, both showed sugar-inducible expression in leaves of transgenic tobacco which occurred via a hexokinase-independent pathway. Analyses using various 5'-terminal and internal deletions of the beta-Amy promoter indicated that truncated promoters of beta-Amy containing a sequence between -901 and -820, relative to the transcription start site, and the basic promoter region can confer sugar-inducible expression. This 82 bp region contained the TGGACGG sequence that plays an essential role in the sugar-inducible expression of the truncated promoter of the sporamin gene. Deletion or base substitutions of this element in the truncated beta-Amy promoter abolished the sugar-inducible expression, the results suggesting that the TGGACGG element plays an important role in the coordinate induction of expression of genes for beta-amylase and sporamin by sugars.
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PMID:Sugar-responsible elements in the promoter of a gene for beta-amylase of sweet potato. 1151 55

Phosphorolysis rather than phosphorylation of amylolysis products was found to be the major pathway of sugar phosphate formation from amylopectin by pea (Pisum sativum L.) chloroplast stromal proteins. The K(m) for inorganic phosphate incorporation was 2.5 mm, and ATP did not stimulate amylopectin-dependent phosphate incorporation. Arsenate (10 mm) inhibited phosphate incorporation into glucose monophosphates up to 46% and phosphoglucomutase activity 96%, resulting in glucose 1-phosphate accumulation as a product of amylopectin degradation. The intracellular distribution of enzymes of starch utilization was determined. Phosphorylase, phosphoglucomutase, and hexokinase were found in the chloroplast and cytoplasm, while beta-amylase was restricted to the cytoplasm. Maltase was not detectable; maltose phosphorylase was active in the chloroplast.
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PMID:Amylopectin degradation in pea chloroplast extracts. 1666 Feb 63

The disaccharide trehalose has dramatic effects on plant metabolism, growth and development. Arabidopsis seedlings grown on trehalose-containing medium without sucrose display increased expression of the starch synthesis gene ApL3, hyper-accumulation of starch in the cotyledons and inhibition of root growth. Here we show that the ABI4 transcription factor mediates the effects of trehalose on starch metabolism and growth, independently of abscisic acid (ABA) synthesis and hexokinase (HXK1) signaling. Surprisingly, although the abi4 mutation partially rescued trehalose inhibition of root elongation, ApL3 expression levels were still enhanced. Gene expression analysis suggests that trehalose affects both starch synthesis and starch breakdown. The expression of genes involved in starch breakdown, such as SEX1 and the beta-amylase gene BMY8/BAM3, was strongly down-regulated in WT plants grown on trehalose but not in abi4 mutants. Addition of trehalose to liquid-grown WT seedlings also significantly reduced SEX1 expression after 6 h. Bypassing the need for starch breakdown by growth in continuous light or addition of sucrose rescued root growth on trehalose medium similar to the abi4 mutation. These results suggest that inhibition of starch mobilization rather than increased synthesis is involved in growth inhibition by exogenous trehalose. Trehalose also significantly enhanced ABI4 expression but reduced its sucrose induction, providing a possible molecular mechanism for the trehalose effect on plant gene expression and growth.
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PMID:ABI4 mediates the effects of exogenous trehalose on Arabidopsis growth and starch breakdown. 1703 12