High molecular weight opioid-containing proteins in striatum.

Striatal extracts of guinea pigs, rats, and cattle were found to contain two large proteins (greater than 40,000 and greater than 100,000 daltons) that on treatment with trypsin yield opioid peptides differing chromatographically from the opioid nonapeptide generated by trypsin digestion of endorphins, beta-lipotropin, or pro-opiocortin. Furthermore, the large opioid proteins found in the pituitary do not appear to be present in the striatum. These and other findings indicate that the striatal enkephalins are produced via a pathway from the one deduced from studies on the pituitary.