Microemulsions enzyme mechanism

Activity and stability are often comparable to values in aqueous media. Many substrates which cannot be made to react in water or in pure organic solvents such as hexane owing to lack of solubility can be brought to reaction in microemulsions. Whereas enzyme structure and mechanism do not seem to change upon transition from water to the microemulsion phase (Bommarius, 1995), partitioning effects often are very important. Besides an enhanced or diminished concentration of substrates in the vidnity of microemulsion droplets and thus of enzyme molecules, the effective pH values in the water pool of the droplets can be shifted in the presence of charged surfactants. Frequently, observed acceleration or deceleration effects on enzyme reactions can be explained with such partitioning effects (Jobe, 1989). 

GYP 3 A4 is the major metabolic pathway for SRL thus the drug interactions mediated by induction or inhibition of the GYP 3A4 enzyme system are similar to those seen with GSA and TAG (see Table 87-6). Administration of the microemulsion formulation of GSA with SRL significantly increases the AC/C and trough SRL levels. The same is not seen with the standard formulation of GSA. Gonversely, GSA concentrations and AUC are also increased by SRL. The mechanism is proposed to be competitive binding to GYP 3A4 and /7-glycoprotein. It is recommended that patients separate the dose of SRL and GSA by 4 hours to minimize the interaction. Goncomitant administration of TAG does not affect SRL levels. ... 

There are various reports in the literature concerning kinetic studies of the Upase-catalyzed hydrolysis or synthesis of esters in microemulsions [8,9,49,83,84]. A simple MichaeUs-Menten kinetic model was proposed for the hydrolysis of triglycerides [85,86], while the esterifications of aliphatic alcohols with fatty acids follow a ping-pong bi-bi mechanism [87]. According to this mechanism the lipase reacts with the fatty acid to form a noncovalent enzyme-fatty acid complex, which is then transformed to an acyl-enzyme intermediate, while water, the first product, is released this is followed by a nucleophile attack (by the alcoholic substrate) to form another binary complex that finally yields the ester and the free enzyme. The kinetic parameters and determined in these studies represent apparent... 

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