Levitsky D I, Nikolaeva O P, Vedenkina N S, Shnyrov V L, Golitsina N L, Khvorov N V, Permyakov E A, Poglazov B F
A N Bakh Institute of Biochemistry, Academy of Sciences of the USSR, Moscow.
Biomed Sci. 1991;2(2):140-6.
Thermal denaturation of myosin subfragment 1 (S1) isoforms from rabbit skeletal muscle containing the different alkali light chains A1 and A2 [S1(A1) and S1(A2), respectively] were studied by various methods. Turbidity measurements showed that thermally induced (heating rate 1 degrees C min-1) aggregation of S1(A1) occurs at lower temperatures than that of S1(A2). However, the temperature dependences of the tryptophan fluorescence spectrum and that for ATPase inactivation were the same for S1(A1) and S1(A2). Thermal denaturation of the S1 isoforms was also studied by differential scanning microcalorimetry with the 'successive annealing' method. Three independently melting cooperative regions (domains) were revealed in the molecules of both isoforms. Heat sorption curves for the S1 isoforms were different only for the most thermolabile domain, which had a maximum at 36 degrees C for S1(A1) and at 40.5 degrees C for S1(A2). Two other peaks had maxima at 46-47 degrees C and 50-51 degrees C for both isoforms. It is proposed that alkali light chains A1 and A2 differently affect the conformation of the most thermolabile domain, which probably does not contain trytophan residues and does not take part directly in the formation of the active site of the S1 ATPase.
通过多种方法研究了来自兔骨骼肌的含有不同碱性轻链A1和A2（分别为S1(A1)和S1(A2)）的肌球蛋白亚片段1（S1）同工型的热变性。浊度测量表明，热诱导（升温速率1℃/分钟）的S1(A1)聚集发生的温度低于S1(A2)。然而，S1(A1)和S1(A2)的色氨酸荧光光谱以及ATP酶失活的温度依赖性是相同的。还采用“连续退火”方法通过差示扫描量热法研究了S1同工型的热变性。在两种同工型的分子中均揭示出三个独立的熔融协同区域（结构域）。S1同工型的热吸收曲线仅在最不耐热的结构域有所不同，该结构域在S1(A1)中于36℃出现最大值，在S1(A2)中于40.5℃出现最大值。两种同工型的另外两个峰在46 - 47℃和50 - 51℃出现最大值。有人提出碱性轻链A1和A2对最不耐热结构域的构象有不同影响，该结构域可能不包含色氨酸残基，也不直接参与S1 ATP酶活性位点的形成。
