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Solvent isotope effect on the differences in structure and stability between normal and deuterated proteins
Author(s) -
Chen ChangHwei,
Tow Fred,
Berns Donald S.
Publication year - 1984
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360230506
Subject(s) - chemistry , isothermal microcalorimetry , solvent , urea , enthalpy , denaturation (fissile materials) , deuterium , kinetic isotope effect , crystallography , differential scanning calorimetry , protein secondary structure , analytical chemistry (journal) , nuclear chemistry , chromatography , organic chemistry , thermodynamics , physics , quantum mechanics , biochemistry
Differential scanning microcalorimetry was used to investigate the enthalpy (Δ H d ) and the temperature ( t d ) of thermal denaturation of normal (nondeuterated) (H‐PC) and deuterated (D‐PC) phycocyanins in D 2 O solvent. Values of t d in D‐PC are about 5–7°C lower than those in H‐PC. The magnitudes of Δ H d in D‐PC are only 21–32% of those in H‐PC. During the protein unfolding, the heat‐capacity changes (Δ C p ) in D‐PC are also lower than those in H‐PC. CD was employed to evaluate the secondary structure and the urea denaturation of these proteins in D 2 O solvent. These proteins have about the same α‐helix content. D‐PC is less resistant to the denaturant urea than is H‐PC. In general, the apparent free‐energy change in the process of protein unfolding at zero denaturant concentration is higher in H‐PC than in D‐PC. Comparisons of the present results for D 2 O solvent with those previously reported for H 2 O reveal that solvent isotope effect essentially does not change the α‐helix content in H‐PC and D‐PC. However, D‐PC or H‐PC has a higher random‐coil content in its secondary structure in D 2 O than in H 2 O. Substitution of H 2 O with D 2 O as the solvent increases t d in both D‐PC and H‐PC, lowers Δ H d in H‐PC, and greatly lowers Δ H d in D‐PC. The deuterium solvent isotope effect does not change Δ C p in H‐PC but lowers Δ C p in D‐PC. In the urea denaturation, the magnitudes of ( C u ) 1/2 in H‐PC and D‐PC are not affected by such a solvent effect, whereas those of Δ G app solare greatly increased. These results are correlated with the structure and stability of the proteins.