A monolayer study on cytochrome b5-phospholipid interactions

Cytochrome b5 has been incorporated into phospholipid monolayers at the air/water interface (Langmuir films). Protein incorporation was followed by monitoring changes in surface pressure at constant film area or by measuring film area changes at constant surface pressure. It was possible to deposit proteolipid films on solid substrates using the Langmuir-Blodgett technique. Using the homologous series of phosphatidylcholines, C10:0-C22:0, it was found that increasing chain-length led to increased cytochrome penetration into the surface film. 125I-labelled cytochrome b5 was used to quantify the degree of protein uptake into the film. Phospholipid/protein ratios of 32 and 60 were determined for dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine, respectively. A molecular area of 790 Å2 was calculated for the hydrophobic segment of cytochrome b5. The results are discussed with reference to other work on protein-phospholipid interactions, in particular to studies on cytochrome b5-liposome systems.