Optical Properties of the Hexon of Adenovirus

The ultraviolet absorbance, circular dichroism (CD) and optical rotatory dispersion of the hexons of adenovirus type 2 have been measured and analyzed in terms of secondary structural features. A curve‐fitting method for the CD spectra from 190 nm to 240 nm indicates 170%‐α‐helical, 26%β, and 56%, “random” conformations; the classical parameter b0, indicates from 15 to 20%α‐helical conformation. The far ultraviolet absorbance indicates considerable hypochromicity in comparison to the absorbance expected from the chromophore composition of the protein, which indicates very high α‐helical content. We have applied corrections for absorbance flattening in the analysis of all the spectra and demonstrate the relatively large magnitude of such corrections in the regions of intense absorbance for this protein complex of molecular weight around 400000. In spite of such corrections, the discrepancy in apparent α‐helical contents indicated by ultraviolet hypochromism and by optical rotatory methods persists.