A soluble autolysin has been isolated from cell walls of exponential (log) phase cultures of Streptococcus faecalis ATCC 9790 by means of gel filtration of trypsin-activated wall lysates. Trypsin and other proteolytic enzymes speed wall autolysis apparently by "activating" the autolysin. The autolysin seems to be closely associated with the wall as virtually complete wall dissolution is a prerequisite for obtaining the enzyme in solution. While the soluble autolysin can act on walls of S. faecalis and Micrococcus lysodeikticus, it is virtually inactive on walls from several other bacterial species, Borohydride reduction indicates P revious studies (Shockman, 1963b(Shockman, , 1965Shockman et al., 1958 Shockman et al., , 1961Toennies and Shockman, 1958;Conover et al., 1966) have demonstrated that cells from exponential phase (log) cultures of Streptococcus faecalis 9790 will autolyze rapidly when placed under environmental conditions which prevent the continued synthesis of cell wall peptidoglycan (mucopeptide, glycopeptide, or murein). Inhibition of peptidoglycan synthesis (resulting in autolysis) can be caused either by the addition of a specific inhibitor, such as penicillin or cycloserine, or by deprivation of a nutritionally essential precursor of wall peptidoglycan, such as L-lysine, D-alanine, aspartic and glutamic acids, or glucose.The potential for cell autolysis reached a maximum toward the end of the exponential growth phase and thereafter the cells became resistant to autolysis (Shockman, 1965). Stationary-phase, valine-deprived (Val) or threonine-deprived (Thr) cultures resist autolysis (Shockman, 1965 ; Shockman et al., 1961).Two observations implicated an enzymatic attack on the rigid and protective cell wall as the initial step in cell autolysis. First, when an osmotically protective agent, such as 0.5 M sucrose, was provided, wallfree spherical, osmotically fragile protoplasts could be obtained from log cells, but not from stationaryphase Thr cells in the absence of an exogenous lytic ~~~
