Abstract

The effect of polyethylene glycol (PEG) on the hydrolytic activity of alpha-chymotrypsin has been studied using p-nitrophenyltrimethyl acetate (PNTMA) as substrate. This substrate requires long times to reach the steady state condition, allowing the measurement by conventional methods of the fast initial "burst" step present on the biphasic catalytic behaviour exhibited by alpha-chymotrypsin. The presence of PEG increases both the initial and steady state rates of the reaction. This increase was observed at all the substrate concentrations employed. A formal Michaelis-Menten treatment under steady state conditions shows that K-M remains almost constant over the range of PEG concentrations studied (up to 20% w/v), whereas k(cat) moderately increases with the increment in PEG concentration. The results obtained in this work are interpreted in terms of the following mechanism: