Microviscosity parameters and protein mobility in biological membranes

Area of Science:

• Membrane biophysics
• Cellular biology
• Biochemistry

Background:

• Cholesterol content significantly influences liposome and biological membrane microviscosity.
• Membrane fluidity is a critical factor affecting protein mobility and cellular function.

Purpose of the Study:

• To determine the microviscosity and flow activation energy of liposomes and biological membranes.
• To investigate the relationship between lipid fluidity and the rotational mobility of concanavalin A receptors in normal and malignant cells.

Main Methods:

• Fluorescence polarization technique using 1,6-diphenyl 1,3,5-hexatriene as a probe.
• Derivation of microviscosity (n), flow activation energy (deltaE), and unit flow volume (V) from temperature profiles.
• Analysis of normal and malignant fibroblasts and lymphocytes.

Main Results:

• Increased cholesterol/phospholipid ratio in liposomes leads to higher microviscosity and lower flow activation energy and unit flow volume.
• Biological membranes exhibit a consistent flow activation energy range (6.5-8.5 kcal/mol) irrespective of cholesterol levels.
• Opposite correlations between lipid fluidity and concanavalin A receptor mobility were observed in fibroblasts and lymphocytes.

Conclusions:

• Biological membranes may maintain constant flow activation energy and unit flow volume through vertical protein movement.
• Lipid fluidity and protein mobility exhibit dynamic interrelations, influencing receptor exposure.
• Malignant cells show altered lipid fluidity and receptor mobility compared to normal cells, with cell-type-specific correlations.