Langmuir-Blodgett films of phycobiliproteins .1. Monomolecular film and conformational studies of R-phycoerythrin

The surface pressure-area (pi-A) isotherm of R-phycoerythrin (R-PE) at the air-water interface has been measured. The results indicate that R-PE on form the monomolecular film. Moreover, the molecule-occupied area extrapolating the linear part of the pi-A isotherm is identical with that when an R-PE molecule is located at the interface with its disk plane parallel to the air-water interface. The transmission electron micrograph (TEM) and the measurement of the thickness of the protein monolayer by ellipsometry show that the orientation of R-PE disk plane on the substrate is parallel to the plane of substrate. Absorption and fluorescence spectra of R-PE LB multilayers were obtained through transferring R-PE monolayer at the air-water interface to the substrates at the proper surface pressure by Langmuir-Blodgett (LB) technique. These spectra of R-PE LB film do not show distinct differences from those in aqueous solution. Comparative studies of circular dichroism (CD) spectra of the protein between in aqueous solution and in LB film show that the changes of the secondary structure of R-PE take place, i.e. the beta-sheet component of the protein increases in the LB films.