Perchlorate Mass Balance

Theoretical Efficiency of Oxygen Production from Chlorite
The production of oxygen from chlorite, as catalyzed by chlorite dismutase, proceeds via the following equation:

Given the measurements below,
[ClO₂^-] = 0.500 M
v_ClO2 = 50.0 mL

The chemical amount of chlorite is given by
n_ClO2 = [ClO₂^-] × v_ClO2 = (0.500 M)(0.0500 L) = 0.0250 mol

Because there is a one-to-one relationship between oxygen and chlorite, the theoretical amount (n_O2) of oxygen produced is given by
n_O2 = n_Cl2 = 0.0250 mol

If we assume SATP, the relationship between the volume and molar amount is given by
V = 24.8 L/mol

Therefore, the theoretical volume of oxygen produced (v_O2T) is given by
v_O2T = V × n_O2 = (24.8 L)(0.0250 mol) = 0.620 L

The experimental results show that the experimental volume of oxygen (v_O2E) produced is 69 mL. Therefore, the efficiency of our reaction is
% efficiency = ^v_O2E⁄_vO2T × 100% = ^0.069mL⁄_0.620L = 11%

Conclusions for Oxygen Production

Based on our data, in our first attempt, our engineered E. coli were able to produce 69 mL of O2 from a standard solution of ClO2- with 11% efficiency at a rate of 0.27 g of O2 per hour. Although our rate of O2 production pales in comparison to NASA’s Mars Oxygen IERSU Experiment (MOXIE), which is able to electrochemically break carbon dioxide to produce oxygen at a rate of 10 g per hour, it is important to note that MOXIE relies on electrical energy to operate and catalyze this reaction. On the other hand, our system, which does not require any external energy source, is able to produce a considerable amount of oxygen, even at its infancy. With more work, possibly by evolving chlorite dismutase to improve its catalytic efficiency, it is possible that we can improve its performance in both efficiency and rate of oxygen production.

However, there are still many limitations in our experiment. Because we performed this experiment in E. coli in vivo, it is possible that the reported results actually underestimate the enzyme’s performance. Because chlorite dismutase is in the cytoplasm and chlorite is added to culture, the chlorite ions must first get through the lipid membrane of the cell into the cytoplasm for the reaction to occur. Given that charged particles have a harder time crossing the lipid membrane, it is possible that the rate of chlorite entry into the cell is slow, limiting the available chlorite within the cytoplasm that can be oxidized by chlorite dismutase. Thus, we need to ensure that the impact of the rate of chlorite transport into the cytoplasm is negligible. Furthermore, it is generally acknowledged that purified proteins will perform better in protein function assays compared to assays performed in whole cells due to possible interference from other cellular components. Additionally, our rate measurement is calculated as the average rate of oxygen production over the 20 minute duration of the experiment. Thus, we need to replicate this experiment with more time points, as well as using different substrate concentrations to ensure reproducibility and determine the kinetic parameters of chlorite dismutase (i.e., kcat and KM).