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| Titel |
The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and Aspergillus niger phytase |
| VerfasserIn |
C. von Sperber, F. Tamburini, B. Brunner, S. M. Bernasconi, E. Frossard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 13 ; Nr. 12, no. 13 (2015-07-14), S.4175-4184 |
| Datensatznummer |
250118021
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| Publikation (Nr.) |
 copernicus.org/bg-12-4175-2015.pdf |
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| Zusammenfassung |
| Phosphorus (P) is an essential nutrient for living organisms. Under
P-limiting conditions plants and microorganisms can exude extracellular
phosphatases that release inorganic phosphate (Pi) from organic
phosphorus compounds (Porg). Phytic acid (myo-inositol
hexakisphosphate, IP6) is an important form of Porg in many
soils. The enzymatic hydrolysis of IP6 by phytase yields available
Pi and less phosphorylated inositol derivates as products. The
hydrolysis of organic P compounds by phosphatases leaves an isotopic imprint
on the oxygen isotope composition (δ18O) of released
Pi, which might be used to trace P in the environment. This study
aims at determining the effect of phytase on the oxygen isotope composition
of released Pi. For this purpose, enzymatic assays with histidine
acid phytases from wheat and Aspergillus niger were prepared using
IP6, adenosine 5'-monophosphate (AMP) and glycerophosphate (GPO4)
as substrates. For a comparison to the δ18O of Pi
released by other extracellular enzymes, enzymatic assays with acid
phosphatases from potato and wheat germ with IP6 as a substrate were
prepared. During the hydrolysis of IP6 by phytase, four of the six
Pi were released, and one oxygen atom from water was incorporated
into each Pi. This incorporation of oxygen from water into
Pi was subject to an apparent inverse isotopic fractionation
(ϵ ~ 6 to 10 ‰), which was similar to that
imparted by acid phosphatase from potato during the hydrolysis of IP6
(ϵ ~ 7 ‰), where less than three Pi
were released. The incorporation of oxygen from water into Pi
during the hydrolysis of AMP and GPO4 by phytase yielded a normal
isotopic fractionation (ϵ ~ −12 ‰), similar to
values reported for acid phosphatases from potato and wheat germ. We
attribute this similarity in ϵ to the same amino acid sequence
motif (RHGXRXP) at the active site of these enzymes, which leads to similar
reaction mechanisms. We suggest that the striking substrate dependency of the
isotopic fractionation could be attributed to a difference in the
δ18O values of the C–O–P bridging and non-bridging oxygen atoms in
organic phosphate compounds. |
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