Comparison of the stability of fish light meromyosins by guanidine hydrochloride denaturation

The guanidine hydrochloride denaturation of light meromyosins (LMMs) of fis h (carp, sardine and greenling) and rabbit was investigated to determine th eir structural stability quantitatively. The circular dichroism (CD) and fl uorescence spectroscopies were applied to monitor denaturation. The CD resu lts indicate that the LMM alpha-helix undergoes a two-step unfolding. The f ree energy of denaturation was calculated based on the linear extrapolation method and the denaturant binding model. Total free energies of the two-st ep unfolding of the alpha-helix are related to the water temperatures in wh ich the fish live and the body temperature of rabbit. The stability of alph a-helical structure of LMM was in the following descending order: rabbit > carp > sardine > greenling. The free energies of denaturation obtained by t ryptophan fluorescence differ from the free energies of the unfolding alpha -helix. The data from the two spectroscopic measurements are discussed alon g with the conformational changes of LMMs. (C) 1999 Elsevier Science Inc. A ll rights reserved.