Interconversion of a - and y - Penicillinase from Bacillus cereus 569

Extracellular penicilhnase from Bacillus cereus 569 was found to exist in two states, an iodine-sensitive state and an iodine-insensitive state. Iodine-sensitive penicillinase is inactivated by 2.5 X 10-a M iodine within 1 min, while the iodine-insensitive enzyme is inactivated at a much slower rate. Approximately 20% of the extracellular penicillinase activity found in crude or partially ptied preparations of penicillmase is iodine-sensitive. The two states of penicillinase were shown to be interconvertible. In the presence of saturated ammonium sulfate, penicillinase is converted quantitatively into the iodine-sensitive state, and, upon removal of the ammonium sulfate, it spontaneously reverts to the iodine-insensitive state. It is concluded that o(and y-penicillinase correspond to the iodine-insensitive and iodine-sensitive penicillinases, respectively, and that the two penicillinases are dBerent states of the same enzyme in dynamic equilibrium. The relative proportion of the two states depends upon the conditions imposed upon the enzyme preparation.