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The kinetics of a two‐state transition of myosin subfragment 1 A temperature‐jump relaxation study
Author(s) -
Lin Shwu-Hwa,
Cheung Herbert C.
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)80614-m
Subject(s) - chemistry , relaxation (psychology) , enthalpy , temperature jump , myosin , kinetics , reaction rate constant , kinetic energy , equilibrium constant , activation energy , crystallography , thermodynamics , analytical chemistry (journal) , chromatography , biochemistry , physics , psychology , social psychology , quantum mechanics
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.