| Abstract: | In addition to the spike-associated host capsule depolymerase, infection by Escherichia coli capsule bacteriophage no. 29 also induces the synthesis of a large bacteriolytic enzyme which has been purified to homogeneity. On incubation of isolated host murein sacculi with this enzyme, no amino groups but reducing sugar groups were liberated, and muraminitol, but no glucosaminitol, was found in the degraded sacculi after subsequent reduction with NaBH4. The bacteriolytic enzyme is thus another lysozyme (mucopeptide N-acetylmuramylhydrolase; EC 3.2.1.17). Electron optical visualization of negatively stained lysozyme specimens showed oblong particles of roughly 4.5 to 5.5 nm in diameter and 15 to 19 nm in length. Although the material tended to dissociate, a crude estimate of its molecular weight (270,000 plus or minus 30,000) could be obtained from these dimensions, from its sedimentation equilibrium, and from its behavior in gel chromatography. After disintegration of homogeneous lysozyme 29 by heating in solution with sodium dodecyl sulfate and dithiothreitol, polypeptides of one size only (about 46,000 dalton, probably six copies per molecule) were found in sodium dodecyl sulfate-polyacrylamide electrophoresis. The amino acid analysis of the enzyme accounted for more than 90% of its dry weight. One percent or less of the bacteriolytic activity in phage 29 lysates was found to be associated with the intact or disrupted virus particles, and a polypeptide of 46,000 daltons was not detected in the virions. These results strongly suggest that, in contrast to the host capsule depolymerase also induced by the same phage, and in spite of its comparatively large size, "lysozyme 29" does not constitute an integral part also of the homologous bacteriophage particles. |
