ORIENTATIONAL AND SPECTROSCOPIC STUDIES OF LANGMUIR-BLODGETT-FILMS OFA PHOTODYNAMIC PIGMENTAL PROTEIN, ALLOPHYCOCYANIN

Langmuir films of allophycocyanin (APC) formed at the air-water interf ace and transferred onto solid supports were studied by means of surfa ce pressure-area (pi-A) isotherms and ellipsometry. The occupied area per molecule extrapolating the linear part of the pi-A Curve is identi cal with that when APC molecules were located at the air-water interfa ce by disk plane parallel to the air-water interface. The thickness of the protein monolayer transferred on the substrate was measured by el lipsometry in order to determine the orientation of APC molecules in t he air-water interface. Through observation of transmission electron m icrograph of APC monolayer, we directly acquired the morphology about the orientation of APC molecules in the Langmuir-Blodgett (LB) films. Absorption spectrum of APC multilayers is different from that in the a queous solution, but the fluorescence is the same as that in its aqueo us solution. Comparative studies of circular dichroism spectra of the protein in aqueous solution and in LB film showed that conformational changes occurred, i.e., the alpha-helical APC molecule in aqueous solu tion is partially transformed into a beta-sheet in LB films.