Piperine, an alkaloid inhibiting the super-relaxed state of myosin, binds to the myosin regulatory light chain.

Piperine, an alkaloid from black pepper, was found to inhibit the super-relaxed state (SRX) of myosin in fast-twitch skeletal muscle fibers. In this work we report that the piperine molecule binds heavy meromyosin (HMM), whereas it does not interact with the regulatory light chain (RLC)-free subfragment-1 (S1) or with control proteins from the same muscle molecular machinery, G-actin and tropomyosin. To further narrow down the location of piperine binding, we studied interactions between piperine and a fragment of skeletal myosin consisting of the full-length RLC and a fragment of the heavy chain (HCF).