The role of DTNB light chain in the contractile properties of skeletal muscle.

The mechanical and molecular dynamical properties of the glycerinated muscle fibres from m. psoas of rabbit were investigated after treatment with 5,5'-dithiobis/2-nitrobenzoate (DTNB). After DTNB treatment the fibre bundles shortened and exerted force in ATP-relaxing solution. The rate of the ATP hydrolysis in relaxation-inducing medium increased significantly after DTNB treatment, and simultaneously the amount of the LC2(DTNB) light chain decreased to 40 per cent of the original value measured by gel electrophoresis. The electron paramagnetic resonance spectra of muscle fibres labelled with maleimide spin label after DTNB treatment exhibited high degree of order of label in rigor, but this order decreased after shortening. The experiments support the assumption that, in vertebrate skeletal muscles, besides the troponin-tropomyosin regulation system which developed later in evolution, the LC2 light chain should maintain some regulatory properties.