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Abstract
Ribonuclease-A (RNase-A) has been a model for studying protein folding and unfolding. However, we show here that its unfolding at neutral pH is complicated by aggregation. Circular dichroism thermal scans showed that reversibility of RNase-A after heating is only about 63%. In accordance with this observation, native-polyacrylamide gel electrophoresis of the sample heated at 75°C showed formation of soluble oligomers. Ammonium sulfate at 0.4 M caused about a 3°C higher melting temperature and nearly complete reversibility, while glycine and NaCl at 0.4 M significantly increased reversibility and decreased aggregation without affecting melting temperature. These results demonstrate that aggregation makes thermal unfolding of RNase-A at least partially irreversible and salts and glycine increase reversibility and decrease aggregation.
