ATc

anhydrotetracycline (ATc) is a tetracycline analog, showing increased (30x) affinity for tet repressor. 42 ng/mL gives induction at half maximum according to an in vitro assay.

Preparing working concentration

According to Nallamsetty and Waugh (2007):

Anhydrotetracycline Prepare a 1,000 times stock solution by dissolving 
in 50% ethanol at 100 ug/ml. Store in a foil-covered tube at -20 °C.

MW = 468.22 g/mole. Thus 1X for the recipe above = 214 nM.

References

Tetracycline analogs affecting binding to Tn10-Encoded Tet repressor trigger the same mechanism of induction.

[1]