In serum, myostatin circulates as part of a latent complex containing myostatin propeptide and/or follistatin-related gene. Myostatin-P is known to bind and inhibit myostatin in vitro. This interaction is relevant in vivo, with a majority (>70%) of myostatin in serum bound to its propeptide. Myostatin-P is negative regulator of myostatin in vivo. rHu Myostatin-P is a 27.8 kDa protein that contains 244 amino acid residues. Source:  Genetically modified E.coli.