Influence on Me2SO and incubation time on papain activity studied using fluorogenic substrates

Papain activity in a buffer containing Me2SO was studied using fluorogenic sub­strates. It was found that the number of active sites of papain decreases with increas­ing Me2SO concentration whereas the incubation time, in a buffer containing 3% Me2SO does not affect the number of active sites. However, an increase of papain in­cubation time in the buffer with 3% Me2SO decreased the initial rate of hydrolysis of Z-Phe-Arg-Amc as well as Dabcyl-Lys-Phe-Gly-Gly-Ala-Ala-Edans. Moreover, an in­crease of Me2SO concentration in working buffer decreased the initial rate of papain-catalysed hydrolysis of both substrates. A rapid decrease of the initial rate (by up to 30%) was observed between 1 and 2% Me2SO. Application of the Michae- lis-Menten equation revealed that at the higher Me2SO concentrations the apparent values of kcat/Km decreased as a result of Km increase and kcat decrease. However, Me2SO changed the substrate binding process more effectively (Km) than the rate of catalysis kcat.