sh-Oligopeptide-133 SP is a single chain human peptide, produced synthetically to be identical to a portion of the protein, Endothelin-3, and contains 21 amino acids consisting of aspartic acid, cysteine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, threonine, tryptophan, tyrosine and valine. The parent protein contains a maximum of 238 amino acids which may contain disulfide bonds and/or glycosylation, and consists of the proper sequence of the 20 standard amino acids.