Barnett V A, Schoenberg M
Laboratory of Physical Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892.
Adv Exp Med Biol. 1993;332:133-8; discussion 138-40. doi: 10.1007/978-1-4615-2872-2_12.
The acto-subfragment-1.ATP state is an important intermediate in the Ca-activated acto-S1 ATPase reaction, suggesting that the myosin.ATP crossbridge seen in muscle fibers similarly may be an important intermediate in the contractile cycle. Treatment of muscle fibers with either para-phenylenedimaleimide (pPDM) or N-phenylmaleimide (NPM) alters the myosin crossbridges so that they bind to the actin filament with about the same affinity as the myosin.ATP crossbridge. Additionally, the treated crossbridges and the myosin.ATP crossbridge have virtually identical attachment and detachment rate constants. Thus the treated crossbridges appear to be reasonable analogues of the weakly-binding myosin.ATP crossbridges of relaxed fibers and studies of the treated fibers may shed some light on the behavior of the physiologically important myosin.ATP crossbridge. We have examined the influence of Ca2+ on the binding and rate constants of pPDM- and NPM-treated weakly-binding crossbridges. In agreement with earlier solution studies, we found almost no Ca-sensitivity of the binding of pPDM- or NPM-treated crossbridges.
肌动蛋白-亚片段1.ATP状态是Ca激活的肌动蛋白-S1 ATP酶反应中的一个重要中间体，这表明在肌肉纤维中看到的肌球蛋白.ATP横桥同样可能是收缩周期中的一个重要中间体。用对苯二马来酰亚胺（pPDM）或N-苯基马来酰亚胺（NPM）处理肌肉纤维会改变肌球蛋白横桥，使其与肌动蛋白丝的结合亲和力与肌球蛋白.ATP横桥大致相同。此外，处理过的横桥和肌球蛋白.ATP横桥具有几乎相同的附着和解离速率常数。因此，处理过的横桥似乎是松弛纤维中弱结合的肌球蛋白.ATP横桥的合理类似物，对处理过的纤维的研究可能会揭示生理上重要的肌球蛋白.ATP横桥的行为。我们研究了Ca2+对pPDM和NPM处理的弱结合横桥的结合和速率常数的影响。与早期的溶液研究一致，我们发现pPDM或NPM处理的横桥的结合几乎没有Ca敏感性。
