Moore R L, Houston M E, Iwamoto G A, Stull J T
J Cell Physiol. 1985 Nov;125(2):301-5. doi: 10.1002/jcp.1041250219.
Myosin light chain (P light chain) is phosphorylated by Ca2+ X calmodulin-dependent myosin light chain kinase. Based on studies with rat skeletal muscles, it has been shown that P light chain phosphorylation correlated to the extent of potentiation of isometric twitch tension. It is not clear whether this correlation exists in rabbit skeletal muscle, which has been the primary source of contractile proteins for biochemical studies. Therefore, phosphorylation of myosin P light chain in rabbit slow-twitch soleus and fast-twitch plantaris muscles in situ was examined. Electrical stimulation (5 Hz, 20 seconds) of plantaris muscle produced an increase in the phosphate content of P light chain from 0.17 to 0.45 mol phosphate/mol P light chain. This increase in phosphate content was accompanied by a 58% increase in maximal isometric twitch tension. Tetanic stimulation (100 Hz, 15 seconds) of rabbit soleus muscle resulted in only a small increase in P light chain phosphate content from 0.02 to 0.10 mol phosphate/mol P light chain, and posttetanic twitch tension did not increase significantly. The correlation between potentiated isometric twitch tension and P light chain phosphorylation in rabbit fast-twitch muscle is similar to that observed in rat skeletal muscle. These results were consistent with the hypothesis that phosphorylation of rabbit skeletal muscle myosin, which results in an increase in actin-activated ATPase activity, may be related to isometric twitch potentiation.
肌球蛋白轻链（P轻链）由Ca2+ X钙调蛋白依赖性肌球蛋白轻链激酶磷酸化。基于对大鼠骨骼肌的研究，已表明P轻链磷酸化与等长收缩抽搐张力增强的程度相关。尚不清楚这种相关性是否存在于兔骨骼肌中，而兔骨骼肌一直是生化研究中收缩蛋白的主要来源。因此，研究了兔慢肌比目鱼肌和快肌跖肌中肌球蛋白P轻链的原位磷酸化情况。对跖肌进行电刺激（5Hz，20秒）后，P轻链的磷酸盐含量从0.17摩尔磷酸盐/摩尔P轻链增加到0.45摩尔磷酸盐/摩尔P轻链。磷酸盐含量的这种增加伴随着最大等长收缩抽搐张力增加58%。对兔比目鱼肌进行强直刺激（100Hz，15秒）后，P轻链磷酸盐含量仅从0.02摩尔磷酸盐/摩尔P轻链小幅增加到0.10摩尔磷酸盐/摩尔P轻链，强直刺激后抽搐张力未显著增加。兔快肌中增强的等长收缩抽搐张力与P轻链磷酸化之间的相关性与在大鼠骨骼肌中观察到的相似。这些结果与以下假设一致，即兔骨骼肌肌球蛋白的磷酸化导致肌动蛋白激活的ATP酶活性增加，可能与等长收缩抽搐增强有关。
