Stull J T, Manning D R, High C W, Blumenthal D K
Fed Proc. 1980 Apr;39(5):1552-7.
Contractile performance of cardiac and skeletal muscles may be regulated by cyclic AMP or Ca2+, two second messengers that stimulate the phosphorylation of specific myofibrillar proteins. Cyclic AMP-dependent protein kinase catalyzed the rapid phosphorylation of a single site in the inhibitory subunit of cardiac troponin in vitro and in perfused hearts. Skeletal muscle troponin was not phosphorylated by this enzyme in vivo. Although there was a correlation between cardiac troponin phosphorylation and the positive inotropic response to catecholamines, a biochemical mechanism that could account for a functional relationship between the two processes has not been discovered. Phosphorylation of skeletal muscle myosin was catalyzed by myosin light chain kinase in the presence of Ca2+ and the ubiguitous, multifunctional Ca2+-dependent regulator protein (CDR). The activation of kinase activity appeared to proceed via a trimolecular reaction process in which Ca2+ bound to CDR and the Ca2+.CDR complex then interacted with the enzyme. In rat extensor digitorum longus muscle, a 1 sec tetanic contraction resulted in phosphorylation of myosin light chain with the maximal phosphate incorporated 20 sec after the contraction. The light chain phosphate content declined slowly and correlated to post-tetanic potentiation of isometric twitch tension. Phosphorylation of skeletal muscle myosin may be important in modulating contraction.
心肌和骨骼肌的收缩性能可能受环磷酸腺苷（cAMP）或钙离子（Ca2+）调节，这两种第二信使可刺激特定肌原纤维蛋白的磷酸化。在体外和灌注心脏中，依赖环磷酸腺苷的蛋白激酶催化心肌肌钙蛋白抑制亚基中单个位点的快速磷酸化。骨骼肌肌钙蛋白在体内不会被这种酶磷酸化。虽然心肌肌钙蛋白磷酸化与对儿茶酚胺的正性肌力反应之间存在相关性，但尚未发现能解释这两个过程之间功能关系的生化机制。在钙离子（Ca2+）和普遍存在的多功能钙离子依赖性调节蛋白（CDR）存在的情况下，肌球蛋白轻链激酶催化骨骼肌肌球蛋白的磷酸化。激酶活性的激活似乎通过一个三分子反应过程进行，其中钙离子与CDR结合，然后Ca2+-CDR复合物与该酶相互作用。在大鼠趾长伸肌中，1秒的强直收缩导致肌球蛋白轻链磷酸化，收缩后20秒掺入的磷酸盐达到最大量。轻链磷酸盐含量缓慢下降，并与强直收缩后等长单收缩张力的增强相关。骨骼肌肌球蛋白的磷酸化可能在调节收缩中起重要作用。
