Human ferritin di-subunit with E coil w/ LacI promoter
This part was created by fusing the heavy chain and light chains (BBa_K1189024BBa_K1189025) of human ferritin together. It is expressed under the lacI promoter (BBa_J04500) and has a his-tag for protein purification. An E-coil (BBa_K1189011) is included in order to allow binding of parts containing the respective K-coil (BBa_K1189010). Characterization of this part was done primarily with commercially purchased ferritin. This ferritin is structurally very similar to our recombinant ferritin and does not differ in its chemical properties (Figure 1).
This construct can be used as a reporter through a modification of the iron core to form Prussian Blue (Figure 2). The resulting molecule can then catalyze the formation of radicals from hydrogen peroxide, which can then cause a colour change in substrates such as TMB or ABTS (Figure 3).
We performed a kinetic analysis of our Prussian blue ferritin. We included a comparison of Prussian blue horse spleen ferritin to regular horse spleen ferritin for both TMB and ABTS (Figures 4, 5). For both of the substrates we can see that normal ferritin has a very low catalytic activity compared to our modified ferritin. Using this data were able to determine the Michaelis-Menten catalytic constants for Prussian blue ferritin with different substrates.
In order to complete our kinetic analysis we had to determine the catalytic properties of our Prussian blue ferritin according to the Michaelis-Menten kinetic model. For these tests we varied the colourimetric substrate concentrations (ABTS and TMB) (Figures 6,7). We also varied the hydrogen peroxide concentration in association with TMB as this the first chemical compound that will react in the system (Figure 8).
Table 1. Catalytic constants for our Prussian blue ferritin