Pressure and Temperature Jump Studies of Protein

• Published in: Berichte der Bunsengesellschaft für physikalische Chemie
• Main Authors: Alberty, R. A., Takahashi, M. T., Diven, W. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1964
• Subjects: Sperm whale
• Online Access: http://dx.doi.org/10.1002/bbpc.19640680840; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fbbpc.19640680840; https://onlinelibrary.wiley.com/doi/pdf/10.1002/bbpc.19640680840

Abstract A pressure‐jump apparatus, built according to the general plan of Strehlow and Becker, has been used to study the rate of conformational changes in bovine plasma albumin (BPA) in the p H range 2.0–3.8 in chloride, thiocyanate and perchlorate media. The relaxation behavior in all three media can be described by an equation of te form: ΔR = r 1 exp (‐ t /τ 1 ) + r 2 · exp (‐ t /τ 2 ) where r 1 and r 2 are constants and ΔR is the change in resistance measured conductimetrically. Both relaxation times are independent of BPA concentration and are strongly p H dependent with τ 1 showing a p H maximum. The BPA molecule bears a lower net charge at any given p H in thiocyanate and perchlorate media since these ions are much strongly bound than is chloride. The simplest mechanism consistent with these results involves a stepwise conversion of an expandable form A to an expanded form C via an intermediate B. A temperature‐jump apparatus, built following Eigen's design, has been used to study the kinetics of binding of various ligands to the heme iron of sperm whale metmyoglobin. The relaxation times for solutions of myoglobin containing imidazole and azide are concentration dependent and, since the equilibrium constants have been determined, the rate constants can be calculated. In the p H range 6 to 8, the bimolecular reactions are much slower than diffusion controlled reactions.