sentences:  ", (+)-pentazocine and (+)-cyclazocine), as well as various structurally and pharmacologically distinct psychoactive chemicals such as haloperidol and cocaine, and neuroactive steroids like progesterone.The mammalian σ1 receptor is an integral membrane protein with 223 amino acids.It shows no homology to other mammalian proteins but strikingly shares 30% sequence identity and 69% similarity with the ERG2 gene product of yeast, which is a C 8-C7 sterol isomerase in the ergosterol biosynthetic pathway.