Abstract
Reactivity of phospholipaseA2 on hydrolysis of phosphatidylcholine in W/O microemulsion was kinetically investigated. The desired solvent combinations were prepared by mixing isooctane (C8*) as the main solvent and 1-butanol (C4), 1-pentanol (C5), 1-hexanol (C6), and 1-octanol (C8) as co-solvents. Mixed organic solvents were designed by the molar ratio of isooctane to co-solvents. We used the hydrophobicity based on logP as an indicator of the mixed organic phase. Its experimental range was from 3.816 to 4.090. The alcohol-free isooctane/PC system had very slight increase of production. When 1-butanol was directly injected into the running isooctane/PC system, the initial reaction rate was dramatically promoted about 150-fold. Hydrolysis was successfully performed by injecting 1-butanol, and the reaction rate was promoted. Initial reaction rate was remarkably promoted in the molar ratio of isooctane:1-butanol=11:0.05 to 0.2. More than the molar ratio of 1-butanol=0.2, the increasing of initial reaction rate was achieved maximum level. These findings strongly suggested that alcohol is a necessary co-solvent for quick initiation, even if it was small addition amounts. As a typical reaction characterization in this investigation, a slight delay of fatty acid production was recognized as the lag phase at the beginning of hydrolysis. It was measured as 45 minutes in alcohol-free isooctane/PC system (logP=4.090). When the hydrophobicity decreased, the lag phase was reduced, i.e. from 45 minutes (logP=4.090, C8*alone) to 1.5 minutes (logP=3.816, C8*:C4=11:1). These results suggested that alcohol functioned not only as a good solvent of PC but also as a promoter of hydrolysis.
