The catalytic hydrolysis of p-nitrophenyl acetate by thermally prepared copolymers of lysine and histidine

Abstract

Copolymers of lysine and histidine were prepared under simulated prebiotic conditions by heating the dry monomers at 195 ° for 1.5 hr. The percentage of histidine incorporated into the polymers (2–25%) was controllable by the varying of the proportions in the reactants (5–50%). The polymers catalyzed the hydrolysis of p-nitrophenyl acetate (NPA); the level of activity (pH 6.8, 1 mM NPA, 30 °) per unit weight of polymer (1.0 mg/ml) was directly proportional to the histidine content of the polymer. Activity values (1.6–13.0 μmoles of p-nitrophenol produced per min per g of polymer) were appreciably higher than those reported previously for copolymers of aspartic acid and histidine (0.5–2.8 μmoles per min per g). Samples of thermal polylysine gave values of 1.3–2.2. The results are interpreted to broaden the experimental basis for concepts concerning the abiotic origins of proteins and enzymes.