Solvent isotope effect on the differences in structure and stability between normal and deuterated proteins

✍ Scribed by Chang-Hwei Chen; Fred Tow; Donald S. Berns

• Publisher: Wiley (John Wiley & Sons)
• Year: 1984
• Tongue: English
• Weight: 540 KB
• Volume: 23
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360230506

✦ Synopsis

Synopsis

Differential scanning microcalorimetry was used to investigate the enthalpy ( m d ) and the temperature ( t d ) of thermal denaturation of normal (nondeuterated) (H-PC) and deuterated (D-PC) phycocyanins in Dz0 solvent. Values of t d in D-PC are about 5-7°C lower than those in H-PC. The magnitudes of A H d in D-PC are only 21-32% of those in H-PC.

During the protein unfolding, the heat-capacity changes (AC,) 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 DzO solvent. These proteins have about the same a-helix content. D-PC is less resistant to the denaturant urea than is H-PC. In general, the apparent freeenergy change in the process of protein unfolding a t zero denaturant concentration is higher in H-PC than in D-PC. Comparisons of the present results for DzO solvent with those previously reported for HzO reveal that solvent isotope effect essentially does not change the a-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 DzO than in H20. Substitution of HzO with DzO as the solvent increases t d in both D-PC and H-PC, lowers f?&d in H-PC, and greatly lowers A H d in D-PC. The deuterium solvent isotope effect does not change AC, in H-PC but lowers AC, in D-PC. In the urea denaturation, the magnitudes of (C,),/z in H-PC and D-PC are not affected by such a solvent effect, whereas those of AGgp are greatly increased. These results are correlated with the structure and stability of the proteins.