title: Resistance of β-casein at the air-water interface to enzymatic cleavage.
abstract: X-ray reflectivity from an air-buffer interfacial β-casein monomolecular film placed on a solution of chymosin (renin) showed unexpectedly slow proteolytic cleavage. To understand this, the separate structures of β-casein and chymosin, the presentation of each molecule to the other at the air/liquid interface, and that of their mixtures is reported. At the air/solution interface, the hydrophobicity of the protein molecules causes orientation and some deformation of the conformation. When β-casein was presented to a chymosin monomolecular interfacial film, the chymosin was largely displaced from the surface, which was accounted for by the different surfactancy of the two molecules at 25 °C. There was no observable proteolysis. In the reverse experiment, a significant enzymatic degradation and the signature of hydrophobic fragments was observed but only at and above an enzyme concentration of 0.015 mg/mL in the substrate. For comparison, the air/solution interface of premixed β-casein with chymosin in phosphate buffer showed that the film was composed of β-casein proteolytic fragments and chymosin.
authors.affiliation: Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia.
authors.forename: Jhih-Min
authors.initials: JM
authors.lastname: Lin
authors.forename: Joo Chuan
authors.initials: JC
authors.lastname: Ang
authors.forename: J W
authors.initials: JW
authors.lastname: White
mesh_terms: D000327:Adsorption; D000388:Air; D000818:Animals; D002364:Caseins / Q000737:chemistry* / Q000378:metabolism*; D002417:Cattle; D012085:Chymosin / Q000737:chemistry / Q000378:metabolism*; D014867:Water / Q000737:chemistry*
chemical_list: D002364:Caseins; D014867:Water; D012085:Chymosin