[Met5]-Enkephalin, amide is an agonist for δ opioid receptors as well as putative ζ (zeta) opioid receptors.Met-enkephalin circulates in several forms, some of which may be derived from proteins other than proenkephalin A, and plasma levels of both free native, and peptidase-derivable Met-enkephalin are modulated physiologically.

木质素是植物细胞壁的主要成分，是一种可再生的芳香族聚合物。木质素具有很强的抗氧化活性。木质素（Lignine）是一种天然的复合生物聚合物，具有生物可降解性和生物相容性。

Pro-Adrenomedullin N20, rat