Insights into the origin of carbonaceous chondrite organics from their triple oxygen isotope composition

Dust grains of organic matter were the main reservoir of C and N in the forming Solar System and are thus considered to be an essential ingredient for the emergence of life. However, the physical environment and the chemical mechanisms at the origin of these organic grains are still highly debated. In this study, we report high-precision triple oxygen isotope composition for insoluble organic matter isolated from three emblematic carbonaceous chondrites, Orgueil, Murchison, and Cold Bokkeveld. These results suggest that the O isotope composition of carbonaceous chondrite insoluble organic matter falls on a slope 1 correlation line in the triple oxygen isotope diagram. The lack of detectable mass-dependent O isotopic fractionation, indicated by the slope 1 line, suggests that the bulk of carbonaceous chondrite organics did not form on asteroidal parent bodies during low-temperature hydrothermal events. On the other hand, these O isotope data, together with the H and N isotope characteristics of insoluble organic matter, may indicate that parent bodies of different carbonaceous chondrite types largely accreted organics formed locally in the protosolar nebula, possibly by photochemical dissociation of C-rich precursors.

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A rapid on-line technique for determination of oxygen isotope composition of nitrogen-containing organic matter and water

Rapid Communications in Mass Spectrometry ◽

10.1002/(sici)1097-0231(199709)11:14<1554::aid-rcm980>3.0.co;2-i ◽

1997 ◽

Vol 11 (14) ◽

pp. 1554-1560 ◽

Cited By ~ 106

Author(s):

G. D. Farquhar ◽

B. K. Henry ◽

J. M. Styles

Keyword(s):

Organic Matter ◽

Oxygen Isotope ◽

Isotope Composition ◽

Oxygen Isotope Composition ◽

On Line

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The oxygen-isotope composition of chondrules and isolated forsterite and olivine grains from the Tagish Lake carbonaceous chondrite

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2010.01.018 ◽

2010 ◽

Vol 74 (8) ◽

pp. 2484-2499 ◽

Cited By ~ 24

Author(s):

S.D.J. Russell ◽

F.J. Longstaffe ◽

P.L. King ◽

T.E. Larson

Keyword(s):

Oxygen Isotope ◽

Carbonaceous Chondrite ◽

Isotope Composition ◽

Oxygen Isotope Composition

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The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and <i>Aspergillus niger</i> phytase

Biogeosciences ◽

10.5194/bg-12-4175-2015 ◽

2015 ◽

Vol 12 (13) ◽

pp. 4175-4184 ◽

Cited By ~ 19

Author(s):

C. von Sperber ◽

F. Tamburini ◽

B. Brunner ◽

S. M. Bernasconi ◽

E. Frossard

Keyword(s):

Aspergillus Niger ◽

Oxygen Isotope ◽

Phytic Acid ◽

Wheat Germ ◽

Isotope Composition ◽

Isotopic Fractionation ◽

Oxygen Isotope Composition ◽

Acid Phosphatases ◽

Enzymatic Assays ◽

Hydrolysis Of

Abstract. 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 (&varepsilon; ~ 6 to 10 ‰), which was similar to that imparted by acid phosphatase from potato during the hydrolysis of IP6 (&varepsilon; ~ 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 (&varepsilon; ~ −12 ‰), similar to values reported for acid phosphatases from potato and wheat germ. We attribute this similarity in &varepsilon; 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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The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and <i>Aspergillus niger</i> phytase

Biogeosciences Discussions ◽

10.5194/bgd-12-5055-2015 ◽

2015 ◽

Vol 12 (6) ◽

pp. 5055-5077

Author(s):

C. v. Sperber ◽

F. Tamburini ◽

B. Brunner ◽

S. M. Bernasconi ◽

E. Frossard

Keyword(s):

Aspergillus Niger ◽

Oxygen Isotope ◽

Inorganic Phosphate ◽

Wheat Germ ◽

Isotope Composition ◽

Isotopic Fractionation ◽

Oxygen Isotope Composition ◽

Acid Phosphatases ◽

Enzymatic Assays ◽

Hydrolysis Of

Abstract. 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 (IP6) is an important form of Porg in many soils. The enzymatic hydrolysis of IP6 by phytase yields plant available inorganic phosphate (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 substrate were prepared. During the hydrolysis of IP6 by phytase, four Pi are released, and one oxygen atom from water is incorporated into each Pi. This incorporation of oxygen from water into Pi is subject to an apparent inverse isotopic fractionation (&varepsilon; ∼ 6 to 10‰), which is similar to that imparted by acid phosphatase from potato during the hydrolysis of IP6 (&varepsilon; ∼ 7‰) where less than three Pi are released. The incorporation of oxygen from water into Pi during the hydrolysis of AMP and GPO4 by phytase yielded a normal isotopic fractionation (&varepsilon; ∼ −12‰), again 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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