THE EFFECT OF PH ON THE FOLDING AND STABILITY OF THE MYOSIN ROD

The far-ultraviolet circular dichroism and fluorescence emission intensities of the myosin rod were studied at pH 2-11, in the absence and presence of guanidine hydrochloride. The protein kept its helicity in this pH range. Its stability in the denaturant was higher at acidic pH than at pH 7. This may be due to favorable interactions involving protonated glutamic acid residues at the interface of the two cc-helical chains of the molecule. At alkaline pH, the fluorescence of the myosin rod was quenched, and the tryptophan region of the protein became less stable in the presence of guanidine hydrochloride, due to ionization of tyrosine residues or other amino acids close to tryptophans in the double-helix arrangement.