Ribonuclease A (RNase A), an unusually well defined enzyme, has been a
test protein in the study of a wide variety of chemical and physical
methods of protein chemistry. These methods have in turn provided many
insights into the functional properties of RNase A, as well as topics
of general interest in protein biochemistry, The presence of four dis
ulfide bonds and the existence of two cis peptide bonds preceding prol
ines in the native state have complicated the analysis of the folding
pathway of RNase A. In this review, we present some new information ab
out the folding of RNase A obtained recently by quench-flow H/D exchan
ge combined with NMR and single-jump and double-jump stopped-flow tech
niques.