Growth and differentiation factor-associated serum protein-1 (GASP-1) is a secreted inhibitory TGF-beta binding protein that contains multiple protease inhibitor structural domains. It is expressed primarily in the ovary, testis, and brain, and can act as a potent soluble inhibitor of myostatin and GDF-11, but not Activin A. The GASP-1 gene encodes a 571 amino acid protein that contains a 29 amino acid secretion signal sequence, and multiple identifiable structural features, including a WAP domain, a follistatin/Kazal domain, an immunoglobulin domain, two tandem Kunitz domains, and a netrin domain. Recombinant Human GASP-1 is a 542 amino acid protein that migrates at an apparent molecular weight of approximately 55-66 kDa by SDS-PAGE analysis under non-reducing conditions. The calculated molecular weight of Recombinant Human GASP-1 is 59.9 kDa.