Bartels E M, Cooke P H, Elliott G F, Hughes R A
Biophysics Group, Open University Oxford Research Unit, Boars Hill, UK.
Biochim Biophys Acta. 1993 May 7;1157(1):63-73. doi: 10.1016/0304-4165(93)90079-n.
A decrease in the net fixed electric charge in the A-bands of cross-striated muscle was observed by Bartels and Elliott [2,10] when the muscle went from the rigor to the relaxed condition. The current work localises the source of the charge decrease by following the net charge on myosin (in the form of concentrated gels) and also myosin rod and light meromyosin gels when the gels are exposed to different concentrations of ATP. The work includes a study of muscle A-bands when the muscle is exposed to the same variations in ATP concentrations as the protein gels. The work shows that (i) Only 100-200 microns ATP is needed to initiate the charge decrease between the rigor and relaxed conditions; (ii) the effect of ATP is seen in the muscle A-band and the myosin and myosin rod gels, but not in LMM gels; (iii) pyrophosphate (PPi) shows a similar charge effect to ATP. ADP does not affect the charge on myosin gels, on the other hand. The results suggest that the charge decrease caused by ATP or PPi is due to ligand interaction with one or more sites on the myosin molecule. This interaction causes a disseminated effect in the protein, and a consequent loss in net negative charge either by a decrease in the absorption, of anions to Saroff sites on the protein, or, less probably, by an increase in the absorption of cations at those sites.
巴特尔和埃利奥特[2,10]观察到，当横纹肌从僵直状态转变为松弛状态时，其A带中的净固定电荷减少。当前的研究通过追踪肌球蛋白（以浓缩凝胶形式）以及肌球蛋白杆和轻酶解肌球蛋白凝胶在暴露于不同浓度ATP时的净电荷，来确定电荷减少的来源。该研究还包括对肌肉A带的研究，此时肌肉暴露于与蛋白质凝胶相同的ATP浓度变化中。研究表明：（i）在僵直和松弛状态之间引发电荷减少仅需100 - 200微米的ATP；（ii）ATP的作用在肌肉A带、肌球蛋白和肌球蛋白杆凝胶中可见，但在轻酶解肌球蛋白凝胶中未观察到；（iii）焦磷酸（PPi）显示出与ATP类似的电荷效应。另一方面，ADP不影响肌球蛋白凝胶上的电荷。结果表明，ATP或PPi引起的电荷减少是由于配体与肌球蛋白分子上的一个或多个位点相互作用。这种相互作用在蛋白质中产生扩散效应，并导致净负电荷的损失，这可能是由于蛋白质上萨罗夫位点对阴离子的吸收减少，或者可能性较小的是由于这些位点对阳离子的吸收增加。
