Physicochemical Analyses of the Bovine Milk Fat Globule Membrane. III. Proton Magnetic Resonance Spectroscopy

High resolution nuclear magnetic resonance spectra were from freeze-dried milk fat globule membranes in D2O. The effect of increasing temperature on spectra of the acetone-extracted membrane was related to thermal behavior of its lipid components. At 33.4C the spectrum of the membrane reflected acetonesoluble lipids. At 50C the spectrum of acetone-extracted membrane was still dominated by signals from lipids, which increased in intensities at from 60 to 120C. No signals attributed to proteins were observed before and after treatment with 8M urea and sodium deoxycholate. However, treatment with a more powerful denaturing solvent, trifluoroacetic acid, resulted in sharp resonances attributable to amino acids. This observation indicated ordered configuration for membrane proteins. Data presented suggested little or no restriction in molecular freedom of protons of the membrane constituents. In this regard bovine milk fat globule membrane contrasted with erythrocyte membrane.