Ja. He et al., ORIENTATIONAL AND SPECTROSCOPIC STUDIES OF LANGMUIR-BLODGETT-FILMS OFA PHOTODYNAMIC PIGMENTAL PROTEIN, ALLOPHYCOCYANIN, Langmuir, 12(7), 1996, pp. 1840-1845
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.