Purification and characterization of benzoyl-L-tyrosine ethyl ester hydrolase from the yolk sac membrane of chicken egg

Abstract

An enzyme which hydrolyzes benzoyl-L-tyrosine ethyl ester (BTEE) was purified from yolk sac membranes of day-18 chick embryos. The purified BTEE hydrolase has a molecular weight of 110 000, being composed of 70 000 and 40 000 subunits, and preferred synthetic substrates for chymotrypsin to those for trypsin. The optimum pH and temperature of this enzyme were 6.5–7.0 and 40 °C, respectively. The Km value for BTEE of the enzyme was 16 mM at pH 6.5 and 30 °C. The enzyme was inhibited markedly by some chymotrypsin inhibitors but scarcely inhibited by trypsin inhibitors. Magnesium ion acted as potent activator, depending on the enzyme purity and its concentration, whereas p-chloromercuribenzoate and zinc ion inactivated the activity markedly. The BTEE hydrolase was found to hydrolyze proteins such as casein and hemoglobin. These data indicated that the enzyme is a proteinase similar to chymotrypsin. This proteinase could act on yolk proteins, suggesting that it plays an important role in the metabolism of yolk at the yolk sac membrane layer.