Seems to play a role in testicular function. May be a trophic hormone with a role in testicular descent in fetal life. Is a ligand for LGR8 receptor (By similarity). Heterodimer of a B chain and an A chain linked by two disulfide bonds. 20% of B chains include an extra N-terminal pentapeptide. Expressed exclusively in Leydig cells of the testis. With 2 artifactual S-carboxymethylcysteines. With pyrrolidone carboxylic acid at Gln-27 and 2 artifactual S-carboxymethylcysteines. With 4 artifactual S-carboxymethylcysteines. Belongs to the insulin family.