國立虎尾科技大學 |

Enzymatic Mechanism, Efficiency, and Environmental Activity of Biological Nitrogen Fixation Revealed by the Natural Abundance of Stable Isotopes.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Enzymatic Mechanism, Efficiency, and Environmental Activity of Biological Nitrogen Fixation Revealed by the Natural Abundance of Stable Isotopes./
Author:	Han, Eunah.
Description:	1 online resource (197 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-12, Section: B.
Contained By:	Dissertations Abstracts International85-12B.
Subject:	Geobiology. -
Online resource:	click for full text (PQDT)
ISBN:	9798382807461

Enzymatic Mechanism, Efficiency, and Environmental Activity of Biological Nitrogen Fixation Revealed by the Natural Abundance of Stable Isotopes.
Han, Eunah.

Enzymatic Mechanism, Efficiency, and Environmental Activity of Biological Nitrogen Fixation Revealed by the Natural Abundance of Stable Isotopes. - 1 online resource (197 pages)

Source: Dissertations Abstracts International, Volume: 85-12, Section: B.

Thesis (Ph.D.)--Princeton University, 2024.

Includes bibliographical references

Nitrogenase is the only natural enzyme capable of supplying new nitrogen (N) to the biosphere. It converts inert atmospheric N2 into bioavailable NH3 using a metal cofactor containing molybdenum (Mo) most prevalently, or vanadium or only iron alternatively. The 15N/14N fractionation during N2 fixation (15εfix) is a key parameter for studying environmental N cycling. In vivo 15εfix varies by cofactor type, but the mechanism determining 15εfix at the nitrogenase active site and in a N2-fixing cell remains unidentified. Additionally, Mo as a cofactor component limits environmental N2 fixation rates in some regions, and the activity of Mo-free alternative nitrogenases has been studied in land ecosystems. This dissertation investigates the 15εfix mechanism and environmental activity of nitrogenase isozymes.Chapter 2 examines an isotopic mechanism of 15εfix using Azotobacter vinelandii. In vivo 15εfix values of natural and mutant nitrogenase (2.5‰ to 7‰) were smaller than the kinetic isotope effect of N≡N bond-break (27‰), and a mutant Mo-nitrogenase with altered N2 access to the active site showed higher in vivo 15εfix than a natural Mo-nitrogenase (6.8‰ vs. 2.5‰). This reveals that (i) the nitrogenase reaction is highly committed to NH3 production, and (ii) enzymatic N2 diffusion limits cellular N2 fixation rate, indicating high catalytic efficiency (high kcat/Km) of in vivo nitrogenase reaction. Diffusion limitation may have evolved to protect the cofactor from O2 driven inactivation during the oxygenation of Earth's atmosphere.Chapter 3 demonstrates that asymbiotic N2 fixation occurs, albeit slowly, in leaf litter and soils of temperate forests. Stable carbon isotopic variability in ethylene produced from acetylene confirmed alternative nitrogenase activity to varying degrees. The N2 fixation rate and alternative nitrogenase contribution showed no clear correlation with the content of Mo, vanadium, and carbon-to-nitrogen ratio, and did not change with Mo amendment, although both in soils changed by adding carbon. Previous studies showed Mo increases N2 fixation and reduces alternative nitrogenase activity. However, this study's results contradict this, suggesting quantity of elemental Mo is not equivalent to bioavailability in environmental settings.These two research projects highlight the catalytic efficiency and environmental activity of nitrogenase isozymes, featuring the technical implication of the natural abundance of stable isotopes in studying microbial N2 fixation.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798382807461Subjects--Topical Terms:

907749
Geobiology.
Subjects--Index Terms:

Alternative nitrogenaseIndex Terms--Genre/Form:

554714
Electronic books.

Enzymatic Mechanism, Efficiency, and Environmental Activity of Biological Nitrogen Fixation Revealed by the Natural Abundance of Stable Isotopes.
LDR:04001ntm a22004097 4500 001 1151754
005 20241118085752.5
006 m o d
007 cr mn ---uuuuu
008 250605s2024 xx obm 000 0 eng d
020 $a 9798382807461
035 $a (MiAaPQ)AAI31296490
035 $a AAI31296490
040 $a MiAaPQ $b eng $c MiAaPQ $d NTU
100 1 $a Han, Eunah. $3 1478576
245 1 0 $a Enzymatic Mechanism, Efficiency, and Environmental Activity of Biological Nitrogen Fixation Revealed by the Natural Abundance of Stable Isotopes.
264 0 $c 2024
300 $a 1 online resource (197 pages)
336 $a text $b txt $2 rdacontent
337 $a computer $b c $2 rdamedia
338 $a online resource $b cr $2 rdacarrier
500 $a Source: Dissertations Abstracts International, Volume: 85-12, Section: B.
500 $a Advisor: Zhang, Xinning.
502 $a Thesis (Ph.D.)--Princeton University, 2024.
504 $a Includes bibliographical references
520 $a Nitrogenase is the only natural enzyme capable of supplying new nitrogen (N) to the biosphere. It converts inert atmospheric N2 into bioavailable NH3 using a metal cofactor containing molybdenum (Mo) most prevalently, or vanadium or only iron alternatively. The 15N/14N fractionation during N2 fixation (15εfix) is a key parameter for studying environmental N cycling. In vivo 15εfix varies by cofactor type, but the mechanism determining 15εfix at the nitrogenase active site and in a N2-fixing cell remains unidentified. Additionally, Mo as a cofactor component limits environmental N2 fixation rates in some regions, and the activity of Mo-free alternative nitrogenases has been studied in land ecosystems. This dissertation investigates the 15εfix mechanism and environmental activity of nitrogenase isozymes.Chapter 2 examines an isotopic mechanism of 15εfix using Azotobacter vinelandii. In vivo 15εfix values of natural and mutant nitrogenase (2.5‰ to 7‰) were smaller than the kinetic isotope effect of N≡N bond-break (27‰), and a mutant Mo-nitrogenase with altered N2 access to the active site showed higher in vivo 15εfix than a natural Mo-nitrogenase (6.8‰ vs. 2.5‰). This reveals that (i) the nitrogenase reaction is highly committed to NH3 production, and (ii) enzymatic N2 diffusion limits cellular N2 fixation rate, indicating high catalytic efficiency (high kcat/Km) of in vivo nitrogenase reaction. Diffusion limitation may have evolved to protect the cofactor from O2 driven inactivation during the oxygenation of Earth's atmosphere.Chapter 3 demonstrates that asymbiotic N2 fixation occurs, albeit slowly, in leaf litter and soils of temperate forests. Stable carbon isotopic variability in ethylene produced from acetylene confirmed alternative nitrogenase activity to varying degrees. The N2 fixation rate and alternative nitrogenase contribution showed no clear correlation with the content of Mo, vanadium, and carbon-to-nitrogen ratio, and did not change with Mo amendment, although both in soils changed by adding carbon. Previous studies showed Mo increases N2 fixation and reduces alternative nitrogenase activity. However, this study's results contradict this, suggesting quantity of elemental Mo is not equivalent to bioavailability in environmental settings.These two research projects highlight the catalytic efficiency and environmental activity of nitrogenase isozymes, featuring the technical implication of the natural abundance of stable isotopes in studying microbial N2 fixation.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2024
538 $a Mode of access: World Wide Web
650 4 $a Geobiology. $3 907749
650 4 $a Environmental science. $3 1179128
650 4 $a Microbiology. $3 591510
650 4 $a Biochemistry. $3 582831
653 $a Alternative nitrogenase
653 $a Molybdenum
653 $a Nitrogen fixation
653 $a Nitrogenase
653 $a Azotobacter vinelandii
655 7 $a Electronic books. $2 local $3 554714
690 $a 0483
690 $a 0768
690 $a 0487
690 $a 0410
710 2 $a ProQuest Information and Learning Co. $3 1178819
710 2 $a Princeton University. $b Geosciences. $3 1183380
773 0 $t Dissertations Abstracts International $g 85-12B.
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31296490 $z click for full text (PQDT)