Nuclear spin effects in biological processes

Abstract

Traditionally, nuclear spin is not considered to affect biological processes. Recently, this has changed as isotopic fractionation that deviates from classical mass dependence was reported both in vitro and in vivo. In these cases, the isotopic effect correlates with the nuclear magnetic spin. Here, we show nuclear spin effects using stable oxygen isotopes (¹⁶O, ¹⁷O, and ¹⁸O) in two separate setups: an artificial dioxygen production system and biological aquaporin channels in cells. We observe that oxygen dynamics in chiral environments (in particular its transport) depend on nuclear spin, suggesting future applications for controlled isotope separation to be used, for instance, in NMR. To demonstrate the mechanism behind our findings, we formulate theoretical models based on a nuclear-spin-enhanced switch between electronic spin states. Accounting for the role of nuclear spin in biology can provide insights into the role of quantum effects in living systems and help inspire the development of future biotechnology solutions.

Keywords: aquaporin; electrolysis; isotope; nuclear spin; spin–statistics.

Fig. 1.

Electrolysis results. (A and B) Linear fit for chiral-covered and bare electrode values, respectively. Goodness of fit: A–${\mathrm{R}}^2=0.999$ , B–${\mathrm{R}}^2=0.976.$ (C) ${\displaystyle \raisebox{1ex}{${\delta }^{17}O$}\!\left/ \!\raisebox{-1ex}{${\delta }^{18}O$}\right.}$ values in the evolved oxygen from fit values (green), or calculated as sample average (blue), with SD shown in error bars. Data from nine experiments in total. Values for the chiral covered electrode are0.5083±0.00127 (fit) and 0.5086±0.00124 (average). For the bare electrode, values are 0.5128±0.00249 (fit) and 0.5127±0.00248 (average). P-values are ≪0.001.

Fig. 2.

AQP experiment- method and results. (A) Schematic of the water entrance process into the cells and the extraction of the intracellular water from the exploded cells used for the measurements. (B) The isotopic concentration ratios between ¹⁷O and ¹⁸O of the intracellular water referred to as cells and the extracellular water referred to as medium, for each of the two sources.

Fig. 3.

Parallel spin pairs can create only triplet O₂, while antiparallel pairs can create either ${\mathrm{H}}_2{\mathrm{O}}_2$ or singlet O₂. Moreover, creation of ${\mathrm{H}}_2{\mathrm{O}}_2$ is thermodynamically favored over creation of singlet O₂.

Fig. 4.

The ratio between the number of MI and the NMI molecules which entered the cell via the AQP channel as a function of the relative difference between the time it takes a singlet or a triplet to move through the channel. Source 1 (A) and source 2 (B) represent the calculated ratios given initial concentrations according to the two different mediums in the experimental part. Shaded areas correspond to error bars; the curves present the central values. As we can see, the calculated values overlap with the experimental results and approach the initial concentration ratios when reaching identity between triplet and singlet transfer rates.