STATE OF TYROSINES OF BOVINE PANCREATIC RIBONUCLEASE IN ETHYLENE GLYCOL AND GLYCEROL

The state of the tyrosines of bovine pancreatic ribonuclease was investigated in aqueous ethylene glycol and glycerol. By spectrophotometry, circular dichroism, and optical rotation, a conformational transition was found at all concentrations of polyol up to and including 97 %. Up to 75% glycol or glycerol, the thermal melting profile by optical rotation is sigmoid, with [a] becoming more negative with rising temperature. At 75% glycol or glycerol no transition is seen; but above 75% the melting profile is bell shaped, with [α] becoming first more positive and then more negative. Light scattering measurements give similar bell-shaped profiles, showing increased and then decreased scattering. The value of Tm extrapolated to neat glycol is close to 25°. All three optical methods show little change in conformation up to 90% glycol or glycerol. Marked changes occur between 90 and 97% polyol. This is confirmed by nitration in glycol, but for glycerol there is little nitration even at 93% glycerol. © 1969, American Chemical Society. All rights reserved.