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    Interfacial complex of alpha-lactalbumin with oleic acid: effect of protein concentration and PM-IRRAS study

    Year: 2020

    Journal: J. Mol. Liq., Volume 319, DEC 1

    Authors: Krajewska, M; Dopierala, K; Wydro, P; Broniatowski, M; Prochaska, K

    Organizations: Ministry of Science and Higher Education, PolandMinistry of Science and Higher Education, Poland

    Keywords: Protein binding; Monolayer penetration; BAMLET complex; Oleic acid; alpha-Lactalbumin

    We used the Langmuir technique to investigate the binding of the bovine alpha-lactalbumin (BLA III) to the oleic acid (OA) monolayer in gastric conditions (pH 2.0 and 36.6 degrees C). Both substances are components of the BAMLET complex, which is beneficial to human health. The monolayer studies have been completed with MM imaging and PM-IRRAS spectra. This paper explores the interfacial behavior of the lipid monolayer in the presence of the protein. It proves that the higher the concentration of protein in the subphase, the higher the increase in the relative surface pressure of the OA monolayer is, until the additional amount of protein affects the maximmum film response. We also discussed the MIP (maximum insertion pressure) value and analyzed the infrared spectra to prove that BLA III interacts with OA at the interface. We focused on the kinetics of the interaction between these components. We noticed that after protein adsorption at the interface (which rate depends on BLA III concentration), the protein penetrates the lipid monolayer, followed by film rearrangement (the protein forces on fatty acid molecules to change their orientation) until finally a stable lipid-protein complex is formed at the air-water interface. This multi-stage process is relevant to the course of a relaxation curve, which demonstrates the monolayer response on protein injection. This paper explores the physicochemical phenomena which fully recognized may open the door to numerous applications of these lipid-protein system. (C) 2020 Elsevier B.V. All rights reserved.
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