Wallimann T, Szent-Györgyi A G
Biochemistry. 1981 Mar 3;20(5):1188-97. doi: 10.1021/bi00508a021.
Specific antibodies directed against the regulatory light chains (R-LC) or essential light chains (SH-LC) of scallop myosin abolished calcium regulation in myofibrils, myosin, and heavy meromyosin by elevating the actin-activated Mg2+-ATPase activity in the absence of calcium. Calcium dependence was completely eliminated at molar ratios of 2.5-3 antibodies bound per myosin. Monovalent anti-R-LC Fab and anti-SH-LC Fab fragments also desensitized myofibrils fully. High Ca2+-ATPase activity remained unaffected by the antibodies. Anti-SH-LC IgG reduced to about one-half the actin-activated Mg2+-ATPase in the presence of calcium and the potassium-activated ethylenediaminetetraacetic acid (EDTA)-ATPase activities. Anti-SH-LC Fab, however, desensitized without inhibiting the actin-activated Mg2+-ATPase. The desensitizing effect of both antibodies was abolished by prior absorption with the homologous myosin light chain. Calcium binding and R-LC and anti-SH-LC IgG's and by anti-SH-LC Fab. The anti-R-LC Fab fragment induced a significant (70%) dissociation of R-LC from myofibrils and myosins with concomitant losses in calcium binding. In contrast, anti-R-LC IgG prevented the dissociation of R-LC from myosin by EDTA. Binding of anti-R-LC IgG to myofibrils was proportional to thier R-LC content. Increased amounts of anti-SH-LC IgG were bound by myofibrils devoid of R-LC. Bound anti-SH-LC antibody significantly inhibited the reuptake of R-LC by EDTA-treated myofibrils as well as the full binding of anti-R-LC antibody. Certain rabbits produced a population of anti-SH-LC antibodies which were specific for this light chain and bound extensively to myosin but failed to desensitize it (nondesensitizing anti-SH-LC antibody). The desensitizing and nondesensitizing anti-SH-LC populations bound to different regions of the SH-LC on the myosin, and the binding of the two types of antibody to the SH-LC was nearly additive. The nondesensitizing SH-antibody inhibited the reuptake of R-LC less, and its binding to myofibrils was not influenced by the absence of R-LC. These studies indicate a direct or indirect involvement of the SH-LC's in myosin-linked regulation, raise the possibility of an interaction between the R-LC and SH-LC, and confirm the regulatory function of the scallop R-LC. A model for a relative location of the two types of light chains and the involvement of the subfragment-2 region of myosin linked regulation is discussed.
针对扇贝肌球蛋白调节轻链（R-LC）或必需轻链（SH-LC）的特异性抗体，通过在无钙条件下提高肌动蛋白激活的Mg2+-ATP酶活性，消除了肌原纤维、肌球蛋白和重酶解肌球蛋白中的钙调节。当每分子肌球蛋白结合2.5 - 3摩尔比的抗体时，钙依赖性被完全消除。单价抗R-LC Fab和抗SH-LC Fab片段也能使肌原纤维完全脱敏。高Ca2+-ATP酶活性不受抗体影响。抗SH-LC IgG在有钙存在时，使肌动蛋白激活的Mg2+-ATP酶活性以及钾激活的乙二胺四乙酸（EDTA）-ATP酶活性降低至约一半。然而，抗SH-LC Fab能使肌原纤维脱敏但不抑制肌动蛋白激活的Mg2+-ATP酶。两种抗体的脱敏作用都可通过与同源肌球蛋白轻链预先吸附而消除。钙结合以及R-LC和抗SH-LC IgG及抗SH-LC Fab的结合情况。抗R-LC Fab片段诱导R-LC从肌原纤维和肌球蛋白上显著解离（70%），同时钙结合能力丧失。相反，抗R-LC IgG可防止EDTA使R-LC从肌球蛋白上解离。抗R-LC IgG与肌原纤维的结合与它们的R-LC含量成正比。不含R-LC的肌原纤维结合了更多的抗SH-LC IgG。结合的抗SH-LC抗体显著抑制了EDTA处理的肌原纤维对R-LC的再摄取以及抗R-LC抗体的完全结合。某些兔子产生了一群抗SH-LC抗体，它们对这种轻链具有特异性，能广泛结合到肌球蛋白上，但不能使其脱敏（非脱敏性抗SH-LC抗体）。脱敏性和非脱敏性抗SH-LC群体结合到肌球蛋白上SH-LC的不同区域，两种类型抗体与SH-LC的结合几乎是相加的。非脱敏性SH抗体对R-LC再摄取的抑制作用较小，其与肌原纤维的结合不受R-LC缺失的影响。这些研究表明SH-LC直接或间接参与了肌球蛋白相关的调节，提出了R-LC和SH-LC之间相互作用的可能性，并证实了扇贝R-LC的调节功能。还讨论了两种轻链相对位置的模型以及肌球蛋白亚片段-2区域在调节中的作用。
