Effects of the new anti-ulcer drug ecabet sodium (TA-2711) on pepsin activity. II. Interaction with substrate protein.

To define the mechanism of the protection by ecabet (TA-2711) of the gastric mucosa from peptic attack, the characteristics of protein binding of this drug and its effect on peptic hydrolysis of substrate proteins were investigated in vitro. Both the binding to proteins and the hydrophobicity of ecabet were dependent on the pH; the lower the pH, the higher both parameters. The percentage of ecabet bound to proteins was nearly constant, being independent of the drug concentration at pH's below 2, indicating that this drug is bound to proteins in a non-specific manner. The activity of peptic hydrolysis of bovine serum albumin (BSA) decreased in the presence of ecabet, and this was not due to the interaction between pepsin and ecabet judging from the kinetic studies. The apparent Km values of peptic hydrolysis of BSA increased depending on the quantity of ecabet bound to BSA. These results suggest that ecabet is bound to substrate proteins by a non-specific hydrophobic interaction to form a complex that is less vulnerable to peptic hydrolysis.