The specific refraction increment of crystalline protein: II. α-Chymotrypsinogen

Abstract

The refractive indices of isoionic crystals of a α-chymotrypsinogen have been measured by microscope interferometry employing two procedures. In principle, the index-values are deduced from measurement of optical path of crystal relative to mother liquor by combining this value with measurements first on an air-bubble 3,4 squeezed to the same thickness as the crystal, and second, on the crystal located inside an airbubble. The two principle refractive indices are 1.483 ± 0.003 and 1.486 ± 0.001 by method 1, and 1.480 ± 0.001 and 1.482 ± 0.001 by method 2. Separate measurements of birefringence by the polarizing microscope gave a value of 0.0039 ± 0.00005. The crystals are orthorhombic; it was not possible to measure the third refractive index. Combining these values with data 5 on the dry weight of protein per unit volume of crystal, the principal specific refraction increments are on average 0.00192 and 0.00195. These values are in fairly good agreement with the value of 0.00185 for dilute solutions of α-chymotrypsinogen.