PENETRATION OF GLUCOSE-OXIDASE INTO ORGANIZED PHOSPHOLIPID MONOLAYERSSPREAD AT THE SOLUTION AIR INTERFACE/

Adsorption of glucose oxidase (GOx) at the solution/air interface in t he presence and in the absence of spread monolayers of dibehenoylphosp hatidylcholine (DBPC) has been monitored by surface tension and surfac e potential measurements. At the monolayer-free interface and at the s olution concentration levels of the enzyme higher than 4 mu g/mL, this adsorption was found to be concentration and time dependent. Below th is threshold concentration value, no decrease in the surface tension c ould be observed. Conversely, in the presence of dibehenoylphosphatidy lcholine (DBPC) monolayers, increments in surface pressure were record ed even at GOx solution concentrations at which no diminution of the s urface tension at the monolayer-free interface was observed. These inc rements in surface pressure decreased with the increase in the initial surface pressure of DBPC monolayers independently of the mode of comp ression of monolayers (addition of DBPC aliquots at constant area or d ynamic compression). The increase in surface pressure following the in jection of GOx molecules beneath a DBPC monolayer has been attributed to the occurrence of a hydrophobic interaction between hydrocarbon cha ins of the phospholipid and the enzyme. The differences in the magnitu de and in the rate of the enzyme penetration into spread DBPC monolaye rs are discussed and modeled with respect to the mode of compression o f monolayers.