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  • 1
    Language: English
    In: Geochimica et Cosmochimica Acta, Jan 15, 2014, Vol.125, p.519(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2013.10.010 Byline: Christian von Sperber, Hajo Kries, Federica Tamburini, Stefano M. Bernasconi, Emmanuel Frossard Abstract: Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (P.sub.i). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of P.sub.i. During the enzymatic hydrolysis an isotopic fractionation (I[micro]) occurs leaving an imprint on the oxygen isotope composition of the released P.sub.i which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from Escherichia coli were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5' monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20-30a[degrees] smaller than for alkaline phosphatases, resulting in a difference of 5-7.5a[degrees] in [delta].sup.18O of P.sub.i depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of P.sub.i can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment. Article History: Received 2 May 2013; Accepted 6 October 2013 Article Note: (miscellaneous) Associate editor: Jon Chorover
    Keywords: Adenosine ; Glycerol ; Enzymes ; Phosphates ; Enzymology ; Hydrolysis
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 2011, Vol.75(15), pp.4216-4227
    Description: Phosphorus (P) availability limits productivity in many ecosystems worldwide. As a result, improved understanding of P cycling through soil and plants is much desirable. The use of the oxygen isotopes associated to phosphate can be used to study the cycle of P in terrestrial systems. However, changes with time in the oxygen isotopes associated to available P have not yet been evaluated under field conditions. Here we present the variations in available-P oxygen isotopes, based on resin extractions, in a semi-arid site that included plots in which the amount of rainfall reaching the soil was modified. In addition, the oxygen isotopes in the less dynamic fraction which is extractable by HCl, were also measured. The δ O of the HCl-extractable phosphate shows no seasonal pattern and corresponds to the average value of the available phosphate of 16.5‰. This value is in the expected range for equilibration with soil water at the prevailing temperatures in the site. The δ O values of resin-extractable P showed a range of 14.5–19.1‰ (SMOW), and evidence of seasonal variability, as well as variability induced by rainfall manipulation experiments. We present a framework for analyzing the isotopic ratios in soil phosphate and explain the variability as mainly driven by phosphate equilibration with soil water, and by the isotopic effects associated with extracellular mineralization. Additional isotopic effects result from fractionation in uptake, and the input to the soil of phosphate equilibrated in leaves. These results suggest that the δ O of resin-extractable P is an interesting marker for the rate of biological P transformations in soil systems.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 3
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 January 2014, Vol.125, pp.519-527
    Description: Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (P ). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of P . During the enzymatic hydrolysis an isotopic fractionation (ε) occurs leaving an imprint on the oxygen isotope composition of the released P which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5′ monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20–30‰ smaller than for alkaline phosphatases, resulting in a difference of 5–7.5‰ in δ O of P depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of P can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Library Location Call Number Volume/Issue/Year Availability
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