Relationship between the Latent Form and the Active Form of the Autolytic Enzyme of Streptococcus faecalis

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A 10-hr starvation of Streptococcus faecalis ATCC 9790 for the amino acids methionine and threonine results in cells which are resistant to autolysis and which contain greatly reduced quantities of both active and latent (proteinase activable) forms of the autolytic enzyme (an N-acetyl-muramide glycanhydrolase). Cell walls were isolated from cells harvested at various times during the recovery from such starvation and were assayed for active and latent forms of the autolysin. Within 10 min of recovery the latent enzyme began to increase. Only after 30 to 60 min did the active enzyme begin to increase; after a similar lag, the cells' proneness to lysis markedly increased. The intracellular localization of both forms of the autolysin was examined, using as an experimental tool the ability of added cell wall to bind autolysin. 14C-lysine-labeled, inactivated cell walls were added to exponential-phase cells, which were then disrupted, and the mixed wall population was isolated. Measurement of the 14C release during wall autolysis indicated that the active enzyme in the cells was not available for binding to the added 14C-labeled walls and was therefore wall-bound in vivo. In contrast, up to 85% of latent autolysin activity was found to have been efficiently bound to the added 14C walls. The results obtained suggest (i) cellular autolysis is a reflection of the level of active enzyme and not of latent enzyme, and (ii) autolysin is synthesized and mainly located in the cytoplasm as an inactive latent precursor (proenzyme) which is transported to sites on the cell wall associated with wall biosynthesis, where it becomes activated.

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