J. Biochem, 1982, Vol. 92, No. 3 673-678
© 1982 Japanese Biochemical Society
research-article |
Effects of Temperature and Cholesterol on Human Erythrocyte Membranes
Department of Chemistry, Faculty of Science, Fukuoka University Nishi-ku, Fukuoka, Fukuoka 814-01
The effects of temperature and cholesterol on the membrane fluidity of human erythrocytes were studied using 5-nitoxide stearic acid (5NS), 12-nitoxide stearic acid (12NS), and 16-nitroxide stearic acid (16NS).
Human erythrocytes and their lipid vesicles were treated in the range of 5–55°C. In erythrocytes, ESR signals for 12NS and 16NS showed line broadening above 40°C, whereas those for 5NS became sharper with increasing temperature as was the case with the signals of lipid vesicles for each label molecule. Lipid extraction from the heated sample caused no radical reduction. Only in 12NS-labeled erythrocytes did a weakly immobilized component and a strongly immobilized component appear. In the time course at 50°C, the former decreased and the latter remained constant. From the ratio of both components, it was found that the interaction of the label molecules with the binding sites was determined by the physical state of the membrane. Furthermore, the dependence on temperature of the molecular motion of the labels in the cell membrane was irreversible above 40°C.
On addition of cholesterol to the membrane, the outer hyperfine splittings for 12NS and 16NS increased but that for 5NS decreased at C/P> 1, perhaps indicating a spread between the head groups of phospholipids by cholesterol.