Cis-Trans equilibrium and kinetic studies of acetyl-L-proline and glycyl-L-proline

✍ Scribed by H. N. Cheng; F. A. Bovey

• Publisher: Wiley (John Wiley & Sons)
• Year: 1977
• Tongue: English
• Weight: 369 KB
• Volume: 16
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1977.360160707

✦ Synopsis

Abstract

By means of carbon‐13 nmr (at 25 MHz) the trans/cis conformer ratio in glycyl‐L‐proline has been measured in aqueous (D~2~O) solution over the temperature range 33–96°C. It is found that Δ__H__^0^ = −4.2 kJ/mole and Δ__S__^0^ = −9.7 J/mole/K.

Measurements of the T~1~ values for the proline ring carbons yielded values consistent with a fast puckering process involving both the β‐ and γ‐carbons.

Measurements of the rate of cis‐trans conformational interconversion in glycyl‐L‐proline, using complete line‐shape analysis for the glycyl α‐carbon resonance, gave values for the trans → cis isomerization as follows: Δ__H__^≠^ = 83.5 ± 0.2 kJ/mole; Δ__S__^≠^ = 0.0 ± 10 J/mole/K. A more approximate determination from coalescence temperature observations gave a value of Δ__G__^≠^ of 82.0 ± 0.4 kJ/mole for this process in acetyl‐L‐proline in aqueous solution. The presence of 12__M__ NaSCN lowered this barrier by ca. 2.6 kJ/mole.

Such measurements are relevant to present theoretical models of the denaturation‐renaturation processes in proteins, in which proline residues may play a key role.