CO₂ Fixation by Mineral‐Leaching Bacteria: Characteristics of the Ribulose Bisphosphate Carboxylase‐Oxygenase of ThiobaciIlus ferrooxidans

Abstract

Thiobacillus ferrooxidans is a microorganism involved in the bacterial leaching of minerals. It fixes CO 2 and uses it as its only carbon source. The growth rate of this microorganism is directly increased by increasing the percentage CO 2 above the normal concentration in air. The specific activity of the ribulose bisphosphate carboxylase‐oxygenase (RuBP carboxylase) of T. ferrooxidans also increases with higher CO 2 concentrations. This enzyme has been purified and characterized. The enzyme has a native M r of 570,000 and is composed of M r 54,000 and M r 15,500 subunits; therefore, it corresponds to a T‐type enzyme with an A 8 B 8 structure. The enzyme has apparent K m values for ribulose bisphosphate of 80 µM and for CO2 of 28 µM. The apparent K m values reported for C0 2 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 14 2 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.