A secreted protein of approximately 131 amino acids (depending on species) that regulates the synthesis of eumelanin (brown/black) pigments in melanocytes. Agouti protein antagonizes the signaling of MELANOCORTIN RECEPTORS and has wide distribution including adipose tissue; gonads; and heart. Its overexpression in agouti mice results in uniform yellow coat color, obesity, and metabolic defects similar to type II diabetes in humans.