– Neurophysin 1 specifically binds oxytocin.; Oxytocin causes contraction of the smooth muscle of the uterus and of the mammary gland. Acts by binding to oxytocin receptor (OXTR). OXT Protein, Human, Recombinant (His) is expressed in yeast with N-6xHis tag. The predicted molecular weight is 11.6 kDa and the accession number is P01178.