α-endorphin is the 1-16 fragment of β-endorphin. It is a substrate for transglutaminase and both α-endorphin and its acetylated form are found in intermediate and anterior lobes of the pituitary. It appears to bind to neuronal opiate receptors, but does not bind to β-endorphin receptors in lymphocytes, vasculature, or vas deferens. Stimulatory effects on immune system function have been reported.