Carbohydrate Metabolism

Beck, Erwin; Hopf, Herbert

doi:10.1007/978-3-642-68752-5_7

Cited by 3 publications

(2 citation statements)

References 120 publications

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“…Investigation of plant tissues has regularly revealed more than one activity of invertase on the basis of different pH optima and solubility characteristics, and intra-or extracellular localization (Beck and Hopf 1982). Purification to homogeneity or to near homogeneity of one or the other form of plant invertase has been achieved in only very few instances (Masuda and Sugawara 1980;Krishnan et al 1985;Singh and Knox 1984;Faye and Ghorbet 1983 a, b) and hence most of our more detailed knowledge of this enzyme comes from studies of yeast and fungal enzymes (Avigad 1982).…”

Section: Invertasementioning

confidence: 99%

Cytosolic and cell-wall-bound acid invertases from leaves of Urtica dioica L.: a comparison

Fahrendorf

Beck

1990

Planta

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Two different forms of acid invertase (EC 3.2.1.26) were extracted from expanding leaves of the stinging nettle (Urtica dioica L.). One form was soluble and could be localized within the cytosol, whereas the other was ionically bound to the cell-wall and could not be detected in protoplasts. Both forms were purified, the latter to homogeneity. Western blotting with antibodies against the pure enzyme from cell walls was positive with the cell-wall enzyme but negative with the soluble form of acid invertase. Both forms are glycoproteins with identical molecular weights of 58 kDa. The Km values for sucrose (raffinose) are 5 mM (4.8 mM) for the soluble and 1.2 mM (3.6 mM) for the cell-wall-bound enzyme. The pH optimum of the latter is slightly more acidic (4.5) than that of the soluble invertase (5.5). Both forms could easily be distinguished by their isoelectric points which were determined at pH 4.6 for the soluble and pH 9.3 for the wall-bound enzyme. When extraction and purification were carried out in the absence of protease inhibitors, both acid invertases showed microheterogeneity ('multiple forms'). However, with benzamidine and phenylmethylsulfonylfluoride as protease inhibitors each invertase produced only one protein band upon isoelectric focusing and gel electrophoresis, respectively.

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Section: Invertasementioning

confidence: 99%

Cytosolic and cell-wall-bound acid invertases from leaves of Urtica dioica L.: a comparison

Fahrendorf

Beck

1990

Planta

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“…1974) that the omission of the above new PP intermediates and enzymes from the Calvin scheme provided further explanations of some of the early criticisms and anomalies of the Calvin pathway scheme (Clark et al. 1974; Stiller 1962; Kandler and Gibbs 1956; Beck and Hopf 1982). …”

Section: Introductionmentioning

confidence: 99%

The metabolic significance of octulose phosphates in the photosynthetic carbon reduction cycle in spinach

Williams

MacLeod

2006

Photosynth Res

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Abstract14 C-Labelled octulose phosphates were formed during photosynthetic 14 CO 2 fixation and were measured in spinach leaves and chloroplasts. Because mono-and bisphosphates of D-glycero-D-idooctulose are the active 8-carbon ketosugar intermediates of the L-type pentose pathway, it was proposed that they may also be reactants in a modified CalvinBenson-Bassham pathway reaction scheme. This investigation therefore initially focussed only on the ido-epimer of the octulose phosphates even though 14 C-labelled D-glycero-D-altro-octulose mono-and bisphosphates were also identified in chloroplasts and leaves.14 CO 2 predominantly labelled positions 5 and 6 of D-glycero-D-ido-octulose 1,8-P 2 consistent with labelling predictions of the modified scheme. The kinetics of 14 CO 2 incorporation into ido-octulose was similar to its incorporation into some traditional intermediates of the path of carbon, while subsequent exposure to 12 CO 2 rapidly displaced the 14 C isotope label from octulose with the same kinetics of label loss as some of the confirmed Calvin pathway intermediates. This is consistent with octulose phosphates having the role of cyclic intermediates rather than synthesized storage products. (Storage products don't rapidly exchange isotopically labelled carbons with unlabelled CO 2 .)A spinach chloroplast extract, designated stromal enzyme preparation (SEP), catalysed and was used to measure rates of CO 2 assimilation with Calvin cycle intermediates and octulose and arabinose phosphates. Only pentose (but not arabinose) phosphates and sedoheptulose 7-phosphate supported CO 2 fixation at rates in excess of 120 lmol h -1 mg -1 Chl. Rates for octulose, sedoheptulose and fructose bisphosphates, octulose, hexose and triose monophosphates were all notably less than the above rate and arabinose 5-phosphate was inactive. Altro-octulose phosphates were more active than phosphate esters of the ido-epimer. The modified scheme proposed a specific phosphotransferase and SEP unequivocally catalysed reversible phosphate transfer between sedoheptulose bisphosphate and D-glycero-Dido-octulose 8-phosphate. It was also initially hypothesized that arabinose 5-phosphate, an L-Type pentose pathway reactant, may have a role in a modified Calvin pathway. Arabinose 5-phosphate is present in spinach chloroplasts and leaves. Radiochromatography showed that 14 C-arabinose 5-phosphate with SEP, but only in the presence of an excess of unlabelled ribose 5-phosphate, lightly labelled ribulose 5-phosphate and more heavily labelled hexose and sedoheptulose mono-and bisphosphates. However, failure to demonstrate any CO 2 fixation by arabinose 5-phosphate as sole substrate suggested that the above labelling may have no metabolic significance. Despite this arabinose and ribose 5-phosphates are shown to exhibit active roles as enzyme co-factors in transaldolase and aldolase exchange reactions that catalyse the epimeric interconversions of the phosphate esters of ido-and altro-octulose. Arabinose 5-phosphate is presented as playing this role...

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Magnetic Fields and Spiral Structure

Beck

1983

Internal Kinematics and Dynamics of Galaxies

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Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20 − 30 µG) and in central starburst regions (50 − 100 µG). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10 − 15 µG) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium. -Faraday rotation measures (RM) of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by meanfield dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with Xshaped patterns are observed. -The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with forthcoming radio telescopes like the Square Kilometre Array.

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Carbohydrate Metabolism

Cited by 3 publications

References 120 publications

Cytosolic and cell-wall-bound acid invertases from leaves of Urtica dioica L.: a comparison

Cytosolic and cell-wall-bound acid invertases from leaves of Urtica dioica L.: a comparison

The metabolic significance of octulose phosphates in the photosynthetic carbon reduction cycle in spinach

Magnetic Fields and Spiral Structure

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