The transient and steady-state behavior of a reversible covalent modification system is examined. When the modifying enzymes operate outside the region of first-order kinetics, small percentage changes in the concentration of the effector controlling either of the modifying enzymes can give much larger percentage changes in the amount of modified protein. This amplification of the response to a...

Several strains of Staphylococcus aureus and Staphylococcus epidermidis, exhibiting characteristic resistance patterns to aminoglycoside antibiotics, were examined. The aminoglycoside-modifying enzymes from these strains were purified by DEAE-Sephadex A-50 chromatography, affinity chromatography, and Sephadex G-100 gel filtration. Three enzymes, a 3'-phosphotransferase III (molecular weight, 31...