EFFECTS OF TETRAMETHYLUREA ON THE TERTIARY STRUCTURE OF LYSOZYME IN WATER

We studied by small angle x-ray scattering (SAXS) the tetramethylurea (TMU) effects on the tertiary structure of lysozyme in water. Samples containing TMU with mass fractions, w, ranging from 0 to 0.7 were anal yzed. The SAXS results clearly demonstrate a structural transition fro m a spheroidal molecule (0 less than or equal to w less than or equal to 0.6) to a highly anisometric molecule for w = 0.7. Additional SAXS results for samples with w = 0.7, from which the TMU was removed, show ed that this transition is reversible. The variation of the maximum di mension of the molecule with w fits an equation corresponding to a ''t wo-state'' model, At w = 0.6 (critical fraction) a mixture of folded ( spheroidal) and unfolded (anisometric) molecules coexists in the solut ion. (C) 1998 American Institute of Physics.