Thiobacillus ferrooxidans is a microorganism involved in the bacterial leaching of minerals. It fixes CO2 and uses it as its only carbon source. The growth rate of this microorganism is directly increased by increasing the percentage CO2 above the normal concentration in air. The specific activity of the ribulose bisphosphate carboxylase‐oxygenase (RuBP carboxylase) of T. ferrooxidans also increases with higher CO2 concentrations. This enzyme has been purified and characterized. The enzyme has a native Mr of 570,000 and is composed of Mr 54,000 and Mr15,500 subunits; therefore, it corresponds to a T‐type enzyme with an A8B8 structure. The enzyme has apparent Km values for ribulose bisphosphate of 80 µM and for CO2 of 28 µM. The apparent Km values reported for C02 of RuBP carboxylases of other thiobacilli are 30‐fold higher. The T. ferrooxidans enzyme can be inhibited by 6‐phosphogluconate. Incubation of a crude extract of T.ferrooxidans with the transition state analog 2‐carboxyarabinitoll 1,5‐bisphosphate and 142 leads to a stably labeled enzyme and allows one to estimate that RuBP carboxylase accounts for 2‐5% of the total protein present in the extract.

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