THE DECAY OF THE FLUORESCENCE ANISOTROPY OF TRYPTOPHAN RESIDUES IN FUNGAL LIPASE FROM HUMICOLA-LANUGINOSA

Pulse nanosecond fluorescence anisotropy decay has been used to study the mobility of tryptophan residues within fungal lipase from Humicola lanuginosa. The decay of emission anisotropy of protein in native, in hibited and mutated form has been investigated in buffered water and 5 0% v/v glycerol solutions, The rotational motions of the lipase were a nalyzed in terms of two different kinetic models. It was found that th e fluorescence emission anisotropy decay can best be described with tw o rotational correlation times : 0.63 and 5.45 ns in water and 0.98 an d 10.70 ns and in 50% v/v glycerol solution. Using the same experiment al conditions the decay of inhibited and mutated H. lanuginosa lipase showed a similar biexponential character. These results are interprete d in terms of local or segmental motion arising from a mass of about 1 083 daltons which corresponds to the 'lid'-helix fragment of the enzym e.