Kinetic and structural analysis of the inhibition of adenosine deaminase by acetaminophen

Kinetic and thermodynamic studies have been made on the effect of acetaminophen on the activity and structure of adenosine deaminase in 50 mM sodium phosphate buffer pH 7.5, at two temperatures of 27 and 37degreesC using UV spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. Acetaminophen acts as a competitive inhibitor at 27degreesC (K-i = 126 muM) and an uncompetitive inhibitor at 37degreesC (K-i = 214 muM). Circular dichroism studies do not show any considerable effect on the secondary structure of adenosine deaminase by increasing the temperature from 27 to 37degreesC. However, the secondary structure of the protein becomes more compact at 37degreesC in the presence of acetaminophen. Fluorescence spectroscopy studies show considerable change in the tertiary structure of the protein by increasing the temperature from 27 to 37degreesC. Also, the fluorescence spectrum of the protein incubated with different concentrations of acetaminophen show different inhibition behaviors by the effector at the two temperatures.