title: Physicochemical studies on pepsin-CTAB interaction: energetics and structural changes.
abstract: The interaction between pepsin and CTAB has been elaborately studied with a number of techniques. The enzyme-induced interaction produced complexes, aggregates, and micelles of CTAB with distinct physicochemical features. It was found that at very low surfactant concentration (much below the critical micellar concentration (cmc) of pure CTAB), the surfactant got adsorbed both in monomeric and lower aggregated forms to the high-energy sites of the native biopolymer, leading to enhanced hydrophobicity of the combine, and hence, lowering of the interfacial (air/solution) tension. This was followed by the formation of a faintly turbid solution of the polymer-surfactant coacervate. The CTAB interacted unfolded pepsin along with the surfactant monomer remained adsorbed at the interface to decrease the interfacial tension (gamma) to a low level to produce a break in the gamma vs log [CTAB] plot prior to the normally observed extended cmc (cmce) in presence of polymers. The cac-like aggregation (as observed in tensiometry and viscometry) was not found in conductometry and microcalorimetry, whereas microcalorimetry evidenced the formation of the cmce of CTAB in the presence of the biopolymer. The CTAB influenced structural features of the pepsin were assessed from spectral, viscometric, and circular dichroism measurements.
authors.affiliation: Centre for Surface Science, Department of Chemistry, Jadavpur University, Kolkata 700032, India.
authors.forename: Tanushree
authors.initials: T
authors.lastname: Chakraborty
authors.forename: Indranil
authors.initials: I
authors.lastname: Chakraborty
authors.forename: Satya P
authors.initials: SP
authors.lastname: Moulik
authors.forename: Soumen
authors.initials: S
authors.lastname: Ghosh
mesh_terms: D001704:Biopolymers / Q000737:chemistry; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008823:Micelles; D010434:Pepsin A / Q000737:chemistry*; D017510:Protein Folding; D013057:Spectrum Analysis; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D014783:Viscosity
chemical_list: D001704:Biopolymers; D002593:Cetrimonium Compounds; D008823:Micelles; D013501:Surface-Active Agents; D010434:Pepsin A; D000077286:Cetrimonium