Calf Pregastric Esterase Catalyzed Hydrolysis of 4-Nitrophenylalkanoates: pH and Temperature Effects

Abstract

A commercial extract from the tongue and epiglottal region of suckling calf was partially purified to yield a calf pregastric enzyme with esterase activity against 4-nitrophenylalkanoate esters (C₂-C₁₂) at 370C, pH 7.2. The Km against 4-nitrophenylacetate was 0.023 mM, however, when 4-nitro-phenyldodecanoate was used as the substrate, the Km was 1.06 AM. The maximum activity was achieved at ca. 1.6 AM, which is similar to its critical micelle concentration. The reactivity is dependent upon pH. A pK of 7.23 which was obtained in the pH range 5.5-9.0 is indicative of a single ionizable residue. The activity dependence upon temperature of the partially purified enzyme was determined within the range of 25°C to 48°C and Eyring parameters were calculated.