Differences in structure and stability between normal and deuterated proteins (phycocyanin)

✍ Scribed by Chang-Hwei Chen; I-Wen Liu; Robert MacColl; Donald S. Berns

• Publisher: Wiley (John Wiley & Sons)
• Year: 1983
• Tongue: English
• Weight: 565 KB
• Volume: 22
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360220414

✦ Synopsis

Differential scanning microcalorimetry was used to investigate the enthalpy ( A H d ) and the temperature (td) of thermal denaturation of normal and deuterated phycocyanins isolated from two blue-green algae, Plectonerna calothrieoides and Phwmidium luridurn. Values of td in deuterated proteins are about 5°C lower than those in normat proteins. The magnitudes of A H d in deuterated proteins are 1%36% lower than in normal proteins. The heatcapacity change (AC,) in protein unfolding is essentially the same (2 kcal/mol/K) for deuterated and normal proteins within the experimental error. A t close to physiological temperature (27"C), the differences in thermodynamic functions in the native and denatured states are much higher in normal proteins than in deuterated proteins. CD was employed to evaluate both the secondary structures and urea denaturation of these two types of proteins. In P. luridurn, deuterated protein is about 8% higher in a-helix content; in P. calothricoides it is not significantly higher. Deuterated proteins are less resistant to the denaturant urea than are normal proteins: the denaturant concentration at the midpoint of the denaturation curve is 0.6-1.2 mol/L lower in the deuterated proteins. The apparent free energies of unfolding of deuterated proteins at zero denaturant concentration are 1.1-1.5 kcal/mol less than for normal proteins.