HYDROLYSIS OF SATURATED SOYBEAN PHOSPHATIDYLCHOLINE IN AQUEOUS LIPOSOME DISPERSIONS

Hydrolysis kinetics of saturated soybean phosphatidylcholine (PC) were investigated as a function of pH, temperature, buffer concentration, buffer species, and ionic strength in aqueous liposome dispersions. A high-performance liquid chromatography method was used to separate PC and the hydrolysis products. Hydrolysis of PC followed pseudo first-order kinetics. Hydrolysis of fatty acid esters at sn-1 and sn-2 positions initially resulted in the formation of 2-acyl lysophosphatidylcholine and 1-acyl lyso-phosphatidylcholine; because of acyl migration, the most stable isomer of lyso-phosphatidylcholine, 1 -acyl lyso-phosphatidylcholine, was formed predominantly. General acid-base catalysis was observed for acetate and Tris ions. The pH profiles at 40 and 70-degrees-C for a buffer concentration of 0.05 M showed a minimum hydrolysis rate at about pH 6.5. The relationship between the observed rate constant and temperature could be described adequately by the Arrhenius equation below and above the phase transition temperature of saturated soybean PC (52-degrees-C).