Intracellular location of the autolytic N-acetylmuramyl-L-alanine amidase in Bacillus subtilis 168 and in an autolysis-deficient mutant by immunoelectron microscopy

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Abstract
Antisera against purified autolytic N-acetylmuramyl-L-alanine amidase from Bacillus subtilis 168 were prepared in rabbits. They neutralized the enzymatic action of the purified amidase acting on isolated sodium dodecyl sulfate (SDS)-treated walls from the same organism. They also inhibited the lysis of native walls, but only after the walls lysed partially. Amidase adsorbed to insoluble walls still combined with antibody. Antisera did not stop the lysis of whole cells. Lowicryl HM20 sections of both strain 168 and its autolytic mutant strain FJ6 were prepared by the progressive-lowering-of-temperature technique, immunolabeled with the antisera, and visualized with colloidal gold particles as markers. The highest concentration of gold particles seemed to be in the septa of dividing cells, followed by the side walls. There was some labeling of the cytoplasm. Adsorption of sera with SDS-treated walls reduced the overall labeling of sections considerably but did not alter the relative intracellular distribution of particles. The results for strains 168 and FJ6 were similar. Labeling of SDS-treated walls unexpectedly revealed the presence of a wall-bound amidase fraction.