Immunochemical properties and intracellular localization of two molecular forms of arginine aminopeptidase in Streptococcus mitis ATCC 9811.

Streptococcus mitis contains two multiple forms of arginine aminopeptidase (I and II) which differ from each other with respect to their content, immunochemical properties and cellular localization. Immunological analyses by Ouchterlony double immunodiffusion and immunoprecipitation showed an antigenic difference between each form by the use of antisera specific for each enzyme. The amounts of enzymes I and II within the cell were estimated to be 230 +/- 4.3 and 646 +/- 20 ng/mg protein (+/- S.D.), respectively, using a standard curve of purified enzyme in a single radial immunodiffusion assay. When intact cells were treated with the cell wall lytic enzyme, N-acetylmuramidase, though both enzymes were solubilized, a time lag was observed for the solubilization of enzyme II. Enzyme I was detected only in the cell wall fraction and showed no detectable associated with the membrane. Although most of the enzyme II activity was recovered in the cell wall fraction, a slight amount (7.5%) of the total activity was also found in the membrane fraction.