Lytic Enzyme from Lysates of Streptomyces venezuelae Infected with Actinophage MSP2

ABSTRACT

A lytic enzyme was purified 600-fold with 12% recovery from lysates of Streptomyces venezuelae S13 infected with actinophage MSP2. The purified enzyme preparation was homogeneous as shown by polyacrylamide electrophoresis. The enzyme was active over a pH range 6.0 to 9.0 with a maximum at pH 7.5. The pH profile for stability was sharp, with an optimum at pH 7.5. Maximal activity occurred between 30 and 35 C. The enzyme was stable at 20 C or less. A 30-min exposure to 25, 30, 35, 40, 45, and 50 C produced an inactivation of 3, 40, 77, 82, 93, and 100%, respectively. Lytic activity was stimulated fivefold by either 5 × 10⁻³m Mg²⁺ or Mn²⁺ and three- and twofold by Ca²⁺ and Ba²⁺, respectively. Addition of Na⁺, K⁺, NH₄⁺, or Li⁺ to the tris(hydroxymethyl)aminomethane-hydrochloride buffer did not alter the rate of lysis. Enzyme activity was inhibited 74 and 27% by 10⁻⁴ and 10⁻⁵m ethylenediaminetetraacetic acid (EDTA), respectively. The inhibition by EDTA was reversed partially by addition of Mg²⁺. Lytic activity was abolished by either 5 × 10⁻⁴m HgCl₂ or p-hydroxymercuribenzoate, whereas 5 × 10⁻⁴m CuSO₄ inhibited 72%. Cell wall solubilization paralleled the release of N-terminal amino groups and reached a level of 0.23 μmole per mg of cell walls. No release of reducing power was detected in treated or untreated cell wall suspensions. Tests for proteolytic activity were negative.