Morphologie et propriétés optiques des cristaux de lysozyme de poule de type quadratique et orthorhombique

Large crystals of hen egg-white (HEW) lysozyme, both tetragonal and orthorhombic, have been studied with a goniometer and optical methods. As the crystals are particularly stable, some of their optical properties have been measured, mainly the refractive indices determined from reflectance measurements under a photometric microscope. Orthorhombic HEW lysozyme: crystals show the faces (010), (011) and (110). Refractive indices n_[001] = n_g = 1-562 to 1.547 (λ = 480-640 nm); n_[100] = n_m = l.560 to 1.544; n_[010] = n_p = 1.550 to 1.532. Maximum birefringence 0.013 (λ) = 589 nm). Optic axial angle 2V =48 to 51°. Tetragonal HEW lysozyme: crystals formed by the association of a tetragonal {110} prism and a {101} tetragonal bipyramid. Refractive indices n_[001] = n_c and n_[100] = n_o, with an aging phenomenon in these crystals, n_e varying between 1-580 and 1.545, n_o between 1.575 and 1.538 (λ = 589 nm). Maximum birefringence 0.007. HEW lysozyme crystals are examples of good-quality protein crystals. Their refractive indices are surprisingly high for organic substances.