Thermally denatured ribonuclease A retains secondary structure as shown by FTIR.
Fourier transform-infrared (FTIR) spectroscopy has been used to test for the presence of nonrandom structure in thermally denatured ribonuclease A (RNase A) at pH* 2.0 (uncorrected pH measured in D2O). The amide I spectral region of the native and thermally denatured protein was compared. A substantial decrease in the amount of beta-sheet and alpha-helix and a corresponding increase in the amount of turn and unordered structure was observed on thermal denaturation. The results indicate that thermally denatured RNase A contains significant amounts of secondary structure (11% helix and 17% beta-sheet), consistent with previous results reported for circular dichroism, and with a relatively compact structure, as revealed by dynamic light scattering. These results are in contrast to those of amide protection experiments reported recently [Robertson, A.D., & Baldwin, R.L. (1991) Biochemistry 30, 9907-9914] which indicated no stable hydrogen-bonded structure under these experimental conditions. Possible explanations for this apparent discrepancy are given.
Seshadri
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Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
Oberg
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Fink
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D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D012259:Ribonuclease, Pancreatic / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
D012259:Ribonuclease, Pancreatic