Time-Structure of the Yeast Metabolism In vivo

Abstract

All previous studies on the yeast metabolome have yielded a plethora of information on the components, function and organisation of low molecular mass and macromolecular components involved in the cellular metabolic network. Here we emphasise that an understanding of the global dynamics of the metabolome in vivo requires elucidation of the temporal dynamics of metabolic processes on many time-scales. We illustrate this using the 40 min oscillation in respiratory activity displayed in auto-synchronous continuously grown cultures of Saccharomyces cerevisiae, where respiration cycles between a phase of increased respiration (oxidative phase) and decreased respiration (reductive phase). Thereby an ultradian clock, i.e. a timekeeping device that runs through many cycles during one day, is involved in the co-ordination of the vast majority of events and processes in yeast. Through continuous online measurements, we first show that mitochondrial and redox physiology are intertwined to produce the temporal landscape on which cellular events occur. Next we look at the higher order processes of DNA duplication and mitochondrial structure to reveal that both events are choreographed during the respiratory cycles. Furthermore, spectral analysis using the discrete Fourier transformation of high-resolution (10 Hz) time-series of NAD(P)H confirms the existence of higher frequency components of biological origin and that these follow a scale-free architecture even in stable oscillating modes. A different signal-processing approach using discrete wavelet transformations (DWT) indicates that there is a significant contribution to the overall signal from ` ~5, ~ 10 and ~ 20-minutes cycles and the amplitudes of these cycles are phase-dependent. Further investigation (derivative of Gaussian continuous wavelet transformation) reveals that the observed 20-minutes cycles are actually confined to the reductive phase and consist of two ~15-minutes cycles. Moreover, the 5 and 10-minutes cycles are restricted to the oxidative phase of the cycle. The mitochondrial origin of these signals was confirmed by pulse-injection of the cytochrome c oxidase inhibitor H(2)S. We next discuss how these multi-oscillatory states can impinge on the apparently complex reactome (represented as a phase diagram of 1,650 chemical species that show oscillatory behaviour). We conclude that biological processes can be considerably more comprehensible when dynamic in vivo time-structure is taken into account.

Systems Biology of the Fluxome

“…Inhibiting mitochondrial respiration at the level of cytochrome oxidase with hydrogen sulfide (H2S) abated all oscillatory frequencies including the 40 min-period ultradian clock. This result provided proof of principle in support of the idea that multi-scale timekeeping is an emergent property of the overall network involved in metabolism, growth and proliferation of yeast [44,60]. This finding also poses the interesting possibility that, in principle, multi-rhythmic processes could be modulated over the whole frequency range.…”

Complex oscillatory redox dynamics with signaling potential at the edge between normal and pathological mitochondrial function

“…Theoretical simulations indicated that the mitochondrial oscillator's period can be modulated over a wide range of time scales (Cortassa et al, 2004; Aon et al, 2006, 2008b). Although the frequency distribution is broad under normal conditions, the long-term temporal correlations of the mitochondrial network could theoretically allow a change in one time scale to be felt across the frequency range, a feasible behavior in systems exhibiting inverse power law relations (Yates, 1992; West, 1999; Aon et al, 2008c; Sasidharan et al, 2012). These results led to the idea that mitochondrial oscillations may play a role as intracellular timekeeper (Aon et al, 2007a; 2008b,c).…”

Network dynamics: quantitative analysis of complex behavior in metabolism, organelles, and cells, from experiments to models and back

“…Both NAD(P)H and ATP show maximum production in the reductive phase. Relationships with mitochondrial function, DNA remodeling and duplication, and the cell division cycle in vivo have been further revealed …”