Bilayer permeability-based substrate selectivity of an enzyme in liposomes

Area of Science:

• Biochemistry
• Biophysics
• Materials Science

Background:

• Liposomes are versatile lipid-based vesicles used in drug delivery and as microreactors.
• Enzyme encapsulation within liposomes creates compartmentalized systems for biochemical reactions.
• Understanding liposome permeability is crucial for controlling enzyme accessibility and substrate specificity.

Purpose of the Study:

• To investigate the substrate selectivity of alpha-chymotrypsin encapsulated within 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes.
• To determine the role of liposome bilayer permeability in enzyme-substrate interactions.
• To evaluate liposomes as microreactors for enzyme-catalyzed reactions with varying substrate sizes.

Main Methods:

• Preparation of liposomes from POPC encapsulating alpha-chymotrypsin.
• Incubation of liposomes with small (benzoyl-l-Tyr-p-nitroanilide, acetyl-l-Phe-p-nitro-anilide) and large (succinyl-l-Ala-l-Ala-l-Pro-l-Phe-p-nitroanilide, casein) substrates.
• Assay of enzyme activity by measuring product formation from substrate hydrolysis.

Main Results:

• The liposome-entrapped alpha-chymotrypsin efficiently hydrolyzed small substrates that could permeate the POPC bilayer.
• Large substrates, unable to cross the liposome membrane, were not hydrolyzed by the encapsulated enzyme.
• A clear correlation was observed between substrate size, liposome permeability, and enzyme activity.

Conclusions:

• Liposome compartmentalization dictates enzyme accessibility and substrate selectivity.
• The permeability of the liposome bilayer acts as a selective barrier, controlling which substrates interact with the entrapped enzyme.
• Liposomes function as effective microreactors, enabling size-selective enzymatic transformations based on their barrier properties.