Introduction
We developed a mathematical model to understand the relationship between the enzymes in our genetic constructs and their immediate microenvironment a priori. Using the MATLAB numerical solver ode23 and kinetic information from in vitro experiments found in literature (Table 1 and 2), we modeled the bioluminescence reaction network as an isolated system under steady state conditions and acquired preliminary light emission results for our different genetic constructs.
Chemical Reaction Network
The microbial Lux system can be interpreted as a two-component module, the aldehyde synthesis pathway and the light production pathway, coupled by an aldehyde and fatty acid.
Figure 1. The reactions in the aldehyde synthesis pathway are tightly coupled by the LuxCDE genes given the 1:1 ratio amongst substrate and product15.
In the aldehyde synthesis pathway (Fig. 1), the transferase (LuxD) first cleaves acyl-ACP and forms a fatty acid (RCOOH), via hydrolysis, which is subsequently activated by the synthetase subunit (LuxE) and reversibly transferred to the reductase subunit (LuxC) before being reduced with NADPH to an aldehyde (RCHO)5,8,18,19,20. The fatty acid activation process in the synthetase subunit occurs at very low levels in the absence of reductase15. However, when the synthetase and reductase subunits are co-expressed with luciferase, the system proceeds to emit light in the absence of transferase16; albeit at lower levels.
LIGHT PRODUCTION PATHWAY
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Modeling
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LIST OF ASSUMPTIONS
SYSTEM OF EQUATIONS
Induction Curves and Parameter Sensitivity
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FIGURES
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Model Reduction
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SYSTEM OF EQUATIONS
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Velocity Equations
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EQUATIONS
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EQUATIONS
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Results
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Future Directions
Parameter Table
Rate Constant | Value | Reference |
---|---|---|
k1 | unknown | |
k2 | unknown | |
k3 | unknown | |
k4 | unknown | |
k5 | unknown | |
k6 | unknown | |
k7 | 21.2 s-1 | (14) |
k8 | 10 s-1 | (9) |
k9 | 6.0*105 M-1s-1 | (12) |
k10 | 4.6 s-1 | (12) |
k11 | 2.4*106 M-1s-1 | (12) |
k12 | 0.1 s-1 | (12) |
k13 | 1.2*105 M-1s-1 | (12) |
k14 | 0.1 s-1 | (12) |
k15 | 9.5 s-1 | (12) |
k16 | 0.5 s-1 | (12) |
k17 | 3*103 M-1s-1 | (2) |
k18 | 0.06 s-1 | (2) |
k19 | 1.9*10-3 s-1 | (3) |
k20 | 1*105 M-1s-1 | (12) |
k21 | 40 s-1 | (12) |
Enzyme Table
Enzyme | Parameter | Value |
---|---|---|
lux AB | VmaxluxAB | 71.58 |
r22 | 0.62 | |
k41 | 0.22 | |
k42 | 81.5 | |
k43 | 72.2 | |
lux EC | VmaxluxEC | 198.93 |
r44 | 0.04 | |
k61 | 90.9 | |
k62 | 95.3 | |
k63 | 24.35 | |
k64 | 76.5 | |
frp | Vmaxfrp | 51.8 |
r12 | 1 | |
k31 | 0.72 | |
k32 | 49.5 | |
lux D | VmaxluxD | 45.8 |
r33 | unknown | |
k51 | 0.37 | |
k52 | unknown |
Cofactor Table
Chemical Species | Concentration (uM) | Reference |
---|---|---|
NADPH | 560 | (6) |
ATP | 1310 | (6) |
O2 | 550 | (27) |
H2O | 500 | unknown |
H+ | 300 | unknown |
Scripts
Link to Enzyme Kinetics Scripts
References
REFERENCES