THE COMPACTNESS OF RIBONUCLEASE-A AND REDUCED RIBONUCLEASE-A

The compactness of ribonuclease A with intact disulfide bonds acid red uced ribonuclease A was investigated by synchrotron small-angle X-ray scattering. The R-g values and the Kratky plots showed that non-reduce d ribonuclease A maintain a compact shape with a R-g value of about 17 .3 Angstrom in 8 M urea, The reduced ribonuclease A is more expanded, its R-g value is about 20 Angstrom in 50 mM Tris-HCl buffer at pH 8.1 containing 20 mM DTT, Further expansions of reduced ribonuclease A wer e observed in the presence of high concentrations of denaturants, indi cating that reduced ribonuclease A is more expanded and is in neither a random coil [A, Noppert et al,, FEES Lett. 380 (1996) 179-182] nor a compact denatured state [T.R. Sosnick and J. Trewhella, Biochemistry 31 (1992) 8329-8335], The four disulfide bonds keep ribonuclease A in a compact state in the presence of high concentrations of urea. (C) 19 98 Federation of European Biochemical Societies.