Abstract

RATIONALE: Earlier experiments demonstrated that isotopic effects during nitrification, denitrification and dissimilatory nitrate reduction can be affected by high N-15 contents. These findings call into question whether the reaction parameters (rate constants and Michaelis-Menten concentrations) are function of delta N-15 values, and if these can also lead to significant effects on the bulk reaction rate.METHODS: Five experiments at initial delta N-15-NO3- values ranging from 0% to 1700% were carried out in a recent study using elemental analyser, gas chromatography, and mass spectrometry techniques coupled at various levels. These data were combined here with kinetic equations of isotopologue speciation and fractionation. Our approach specifically addressed the combinatorial nature of reactions involving labeled atoms and explicitly described substrate competition and time-dependent isotopic effects.RESULTS: With the method presented here, we determined with relatively high accuracy that the reaction rate constants increased linearly up to 270% and the Michaelis-Menten concentrations decreased linearly by about 30% over the tested delta N-15-NO3- values. Because the parameters were found to depend on the N-15 enrichment level, we could determine that increasing d delta N-15-NO3- values caused a decrease in bulk nitrification, denitrification and dissimilatory nitrate reduction rates by 50% to 60%.CONCLUSIONS: We addressed a method that allowed us to quantify the effect of substrate isotopic enrichment on the reaction kinetics. Our results enable us to reject the assumption of constant reaction parameters. The implications of d-dependent (variable) reaction parameters extend beyond the study-case analysed here to all instances in which high and variable isotopic enrichments occur. Copyright (C) 2012 John Wiley & Sons, Ltd.

Published in

Rapid Communications in Mass Spectrometry
2012, Volume: 26, number: 4, pages: 430-442
Publisher: WILEY

UKÄ Subject classification

Analytical Chemistry


Publication identifier

DOI: https://doi.org/10.1002/rcm.6119

Permanent link to this page (URI)

https://res.slu.se/id/publ/111714