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From 2013.igem.org

Modelagem

Contents 1 Modeling TMAO system 1.1 Labels and conventions 1.2 First Modeling 1.3 Second Modeling 2 Modeling IMA System 2.1 First Reaction - Cobalt ions bind to albumin 2.2 Second Reaction - The entry of cobalt in the cell 2.3 Third Reaction - Transcription 2.4 Model simulations

Modeling TMAO system

Labels and conventions

C_E: The enzymatic complex formed by TorT+TorS+TMAO, which reacts with TorR

C: intermediate component of the final enzymatic process

P: Product of the enzymatic reaction

C_TS: Complex formed by TorT and TorS

C_TSM: Complex formed by TorT+TorS and one molecule of TMAO

C_TSM: Complex formed by TorT and TMAO

First Modeling

This is the simplest modeling process to be considered in our study. The product of the enzymatic process is collapsed in only one reaction that was placed at equilibrium.

Imposing the equilibrium in the first reaction we have:

The value of C_E is the initial enzyme concentration for the subsequent enzymatic reactions.

Regarding the enzymatic reaction:

The following relation holds E₀ = C_E + C. And as usual imposing the steady state condition:

With C_E = E₀ - C

Solving for C:

with

In conclusion, we find:

Second Modeling

It was used the same pattern of reactions as before, but with a standpoint of "essential activation" (the first reaction is no longer considered to equilibrium). Some enzymes need to be activated to bind the substrate. In our case, the enzyme is activated by TorS and activators are TMAO and TorT. The rate of product P appearance depends on the activators concentration. The equation that varies with respect to the previous case is:

The total concentration of the enzyme is:

Then we considered and imposed and

The system of equations also comes from:

Defining and replacing we have:

In conclusion the rate of product appearance results

Modeling IMA System

First Reaction - Cobalt ions bind to albumin

The cobalt ion binds to albumin protein, originating the cobalt-albumin complex. If the albumin is derived from a healthy patient, it will bind more cobalt ions than a albumin derived from a patient with heart disease. It happens because patients with heart conditions will have a isquemic modified albumin (IMA), which has less capability of binding to cobalt. Thus, the amount of free cobalt in the system will be determined by the presence of a normal or ischemic albumin in the sample.

Second Reaction - The entry of cobalt in the cell

There are four cobalt transporters in the cell. The rcnA (Uniprot code: P76425) and zntA (Uniprot code: P37617) transport the cobalt to outside the cell. The corA (Uniprot code: P0ABI4) and zupT (Uniprot code: P0A8H3) transport the cobalt to inside the cell.

The equation for the cobalt flux through these transporters is:

Third Reaction - Transcription

In our modeling, we considered the cobalt acting as a transcriptional activator in order to simplify our model.

The transcriptional activation are accessed by the equation:

The transcription and translation are accesed by the equations:

Model simulations

The simulation showed that for lower concentrations of albumin, the initial concentration of cobalt has an influence in the time of reporter protein appearance and it will be detected faster. Nevertheless, for higher concentrations of albumin, the initial concentration of cobalt doesn't have effect in the time of reporter protein appearance, and it will take more time to be detected.

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