Aminopeptidase II from Bacillus stearothermophilus.

1. The low molecular weight aminopeptidase (aminopeptidase II) from Bacillus stearothermophilus cells grown at 50 degrees C was purified to a homogeneous state. 2. Molecular weight determination by sodium dodecyl sulfate gel electrophoresis resulted in a value of 46 000 for the subunits. A molecular weight of 80 000-100 000 has been reported for the native enzyme. We therefore conclude that aminopeptidase II is a dimeric enzyme. 3. The amino-terminal sequence, the amino acid analysis and the subunit molecular weight of aminopeptidase II show no relationship to the corresponding data of aminopeptidase I. 4. Aminopeptidase II binds two Co2+ per subunit. The dissociation constants of these ions determined by binding studies and by kinetic analysis agree within experimental error.