Multi-factorial in vivo stable isotope fractionation: causes, correlations, consequences and applications

Abstract

Many physical and chemical processes in living systems are accompanied by isotope fractionation on H, C, N, O and S. Although kinetic or thermodynamic isotope effects are always the basis, their in vivo manifestation is often modulated by secondary influences. These include metabolic branching events or metabolite channeling, metabolite pool sizes, reaction mechanisms, anatomical properties and compartmentation of plants and animals, and climatological or environmental conditions. In the present contribution, the fundamentals of isotope effects and their manifestation under in vivo conditions are outlined. The knowledge about and the understanding of these interferences provide a potent tool for the reconstruction of physiological events in plants and animals, their geographical origin, the history of bulk biomass and the biosynthesis of defined representatives. It allows the use of isotope characteristics of biomass for the elucidation of biochemical pathways and reaction mechanisms and for the reconstruction of climatic, physiological, ecological and environmental conditions during biosynthesis. Thus, it can be used for the origin and authenticity control of food, the study of ecosystems and animal physiology, the reconstruction of present and prehistoric nutrition chains and paleaoclimatological conditions. This is demonstrated by the outline of fundamental and application-orientated examples for all bio-elements. The aim of the review is to inform (advanced) students from various disciplines about the whole potential and the scope of stable isotope characteristics and fractionations and to provide them with a comprehensive introduction to the literature on fundamental aspects and applications.

Keywords:

• plants
• animals
• isotope biochemistry
• metabolism
• isotope ecology
• hydrogen-2
• carbon-13
• nitrogen-15
• oxygen-18
• sulphur-34

Acknowledgements

The authors are very grateful to Prof. Karl Auerswald (Lehrstuhl für Grünlandlehre der TU München, Germany) for valuable advice and helpful discussions on questions of isotope discrimination by photosynthesis. We are also very grateful to two well-informed and benevolent reviewers, whose advice contributed to the clarity and the rounding off of the manuscript. H-L Schmidt warmly thanks all contributors to the special anniversary issue dedicated to his 85th birthday.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 https://web.stanford.edu/group/Zarelab/publinks/675.pdf

2 The different definitions, as outlined in Boxes A1 and A2, are in use, depending on discipline, regardless of others and without special indications. This is similar for ε, which had originally been defined as ε = k/k*−1. As this causes great confusion, careful attention must be paid to the way that α has been defined.