The kinetics of a two‐state transition of myosin subfragment 1 A temperature‐jump relaxation study

FEBS Letters

Lin, Shwu-Hwa²  Cheung, Herbert C.¹ 

[1] Deaprtment of Biochemistry, University of Alabama at Birmingham, UAB Station, Birmingham, AL 35294-2041, USA;Graduate Program in Biophysical Science, University of Alabama at Birmingham, UAB Station, Birmingham, AL 35294-2041, USA

关键词: Temperature jump;    Myosin subfragment 1;    SI;    myosin subfragment 1;    1AF;    (iodoacetamido)-fluorescien;    SI-AF;    SI labeled with IAF;    TES;    N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid;    εADP;    1;    N o-ethenoadesine 5′-diphosphate;   

DOI  :  10.1016/0014-5793(92)80614-M

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Temperature-jump measurements were carried out on myosin subragment 1 (S1) labeled at Cys-707 with 5-(iodoacetamido)fluorescein (S1-AF). The relaxation was monitored by following the increase in the fluorescence intensity of the attached probe after a jump of 5.8°C. A single relaxation process was observed over a range of final temperatures, and the relaxation time decreased from 16.69 ms at 15°C to 3.91 ms at 27°C. The relaxation results are interpreted in terms of a two-state transition: (S1-AF)_L (S1-AF)₁₁, and the observed single relaxation time (τ) equals 1/(k ₊ + k ₋). The individual first-order rate constants, k ₊ and k ₋, were calculated from τ and the equilibrium constant previously determined. The activation energy was 21.9 kcal/mol for the forward reaction and 9.3 kcal/mol for the reverse reaction, corresponding to an enthalpy value of 12.6 kcal/mol for the two-state transition. The results provide, for the first time, direct kinetic evidence of a two-state transition of S1 in the absence of bound nucleotide, and support a two-state model of unliganded myosin subfragment 1.

【 授权许可】

Unknown