Catalyzes the hydrolysis of the amide bond of streptolidine lactam, thereby conferring streptothricin (ST) resistance. Can hydrolyze streptothricin-F and streptothricin-D. However, this strain is believed to be a ST nonproducer, which raises the possibility that its true role may not be its involvement in self-resistance to STs. May catalyze the hydrolysis of naturally occurring cyclic amide compounds that are structurally related to STs. H2O + streptothricin F = streptothricin F acid Does not require a metal cofactor. Optimum pH is 6.5. Optimum temperature is 45 degrees Celsius. Homodimer. Belongs to the isochorismatase family. Truncated N-terminus.