The production by Arthrobacter sp. of a 30-kDa surface protein and a 25-kDa cytoplasmic protein was increased by the presence of MnO2 in the medium. This high production was also observed in the presence of MnO4- (Mn VII). N-terminal and partial internal sequences of the 30-kDa surface protein have shown no homology with other known proteins. The role of this protein is still unknown, but its highly induced synthesis is possibly related to the binding or the processing of manganic ion by the cells. The 25-kDa cytoplasmic protein has been identified by its N-terminal matching sequence as a superoxide dismutase isoenzyme (Mn-SOD). SOD activity measurements performed on cytoplasmic fractions are related to the protein amounts observed by gel electrophoresis. Arthrobacter sp. synthesized and exhibited SOD activity in both aerobic and anaerobic conditions, thus suggesting other or additional physiological functions for this enzyme.
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