title: Geometric constraints at the surfactant headgroup: effect on lipase activity in cationic reverse micelles.
abstract: The primary objective of the present article is to understand how the geometric constraints at the surfactant head affect the lipase activity in the reverse micellar interface. To resolve this issue, surfactants were designed and synthesized, and activity was measured in /water/isooctane/n-hexanol reverse micellar systems at z ([alcohol]/[surfactant])=5.6, pH 6.0 (20 mM phosphate), 25 degrees C across a varying range of W0 ([water]/[surfactant]) using p-nitrophenylalkanoates as the substrate. It was observed that lipase activity increases from surfactants to with the increment in surface area per molecule (Amin) because of the substitution by the bulky tert-butyl group at the polar head. However, the activity was found to be similar for despite an enhancement in the hydrophilic moieties at the interface. This unchanged lipase activity is presumably due to the comparable surface area of to originating from the rigidity at the surfactant head. Noticeably, the enzyme activity improved from with the simultaneous increment of both the hydroxyl group and the flexibility of the headgroup whereas that for increased exclusively with the flexibility of the headgroup. The common parameter in both groups of surfactants and is the flexibility of the headgroup, which possibly enhance Amin and consequently the lipase activity. Thus, the geometric constraints at the surfactant headgroup play a crucial role in modulating the lipase activity profile probably because of the variation in interfacial area.
authors.affiliation: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata - 700032, India.
authors.forename: Rajendra Narayan
authors.initials: RN
authors.lastname: Mitra
authors.forename: Antara
authors.initials: A
authors.lastname: Dasgupta
authors.forename: Debapratim
authors.initials: D
authors.lastname: Das
authors.forename: Sangita
authors.initials: S
authors.lastname: Roy
authors.forename: Sisir
authors.initials: S
authors.lastname: Debnath
authors.forename: Prasanta Kumar
authors.initials: PK
authors.lastname: Das
mesh_terms: D002384:Catalysis; D002412:Cations; D002861:Chromobacterium / Q000201:enzymology; D004655:Emulsions; D007700:Kinetics; D008049:Lipase / Q000378:metabolism*; D008823:Micelles; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D002412:Cations; D004655:Emulsions; D008823:Micelles; D013501:Surface-Active Agents; D008049:Lipase