Characterization of the subunits of swine kidney leucine aminopeptidase

Abstract The swine kidney leucine aminopeptidase obtained in this study was found to have a molecular weight of 255 000 ± 5000, by the Yphantis method. The subunit, obtained in 6 M guanidine, 0.5% β-mercaptoethanol, has a molecular weight of 63 500 as determined by the Yphantis method. The enzyme is probably converted to a lower molecular weight species, s 20, w = 6.0 S from the native enzyme s 20, w = 13.1 S when dialyzed against 4 M urea, 0.05 M Tris solution. At the same time the enzyme is inactivated. When dialyzed against 4 M urea, 0.05 M Tris and 0.05 M MgCl 2 , the enzyme is not converted to the 6.0-S species and retains full enzymic activity. Dialysis of the enzyme against 0.5 mM EDTA (pH 8.0) completely inactivated it and converted it to a s 20, w = 5.5-S protein. It had been demonstrated earlier that 0.05 M barbital and 0.5 mM MgCl 2 protected the enzyme against inactivation by 5 mM EDTA. These results indicate a potential role for Mg 2+ in subunit structure of the leucine aminopeptidase similar to the role suggested by Simpson and Vallee 12 for zinc in alkaline phosphatase.