Team:Valencia/Modeling

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Oxidative phosphorylation model coupled with thermogenine expression

Our project tries to implement a controlled heating system inside Saccharomyces cerevisiae. The main variables to be taken into account are temperature production and ATP flow. We need to formulate an effective model for the oxidative phosphorylation that couples the genetic expression of the thermogenine with the efficiency of the respiratory chain in ATP production. It will allow us to evaluate the effect produced by thermogenic activity on the energy flow.

Notwithstanding the lack of a specific respiratory chain model in yeast, we are trying to develop our differential equations based on kinetic data collected from the literature. We will later compare our model with other sets of differential equations thought to describe the behavior of skeletal muscle mitochondrion.

Calculating the maximal attainable temperature

Since we need to control the system with the maximal accuracy we should know the theoretical limits of the heating production. Obviously, the minimal temperature value is the corresponding to the culture conditions. The maximal temperature can be determined by supposing that the proton motrive force is used solely in heat production mediated by thermogenine. The following calculations were made taking into account this assumption.

To calculate the energy produced per proton dissipated through the thermogenine we used the published rate (Milakovik et al 2005) of ATP flow as an estimation of the Saccharomyces cerevisiae real value.

17.5 nmol/min = 2.92 • 10 ^-10 mol/s = 1.76 •10¹⁴ ATP particles/s

If ATP synthase needs four protons to produce one molecule of ATP, then we can easily calculate the proton flow through complex V.

7.03 •10¹⁴ p⁺/s

The free energy associated to a single proton being dissipated through the ATP synthase is 20 Kj/mol. Balancing the units we get the energy dissipated per proton:

3.32 •10²³ Kj/p⁺

The energy flow is calculated by multiplying both figures and adjusting the result to the proper units:

2.33 •10^-5 J/s

Reference

Milakovi T. and Johnson G. V. W.2005. Mitochondrial respiration and ATP production are significantly impaired in striatal cells expressing mutant huntingtin. The Journal of Biological Chemistry. 280:30773-30782.