+H2N-Tyr-Gly-Gly-Phe-Met-COO +H2N-Tyr-Gly-Gly-Phe-Leu-COO Met-脑啡肽 Leu-脑啡肽 Cys Tyr iLe S Phe S GIn GIn Asn Asn cys cys Pro Pro Leu Arg Gly -NH2 Gly -NH2 牛催产素 牛力加玉素 +H3N-Tyr-Gly-Gly-Phe-Met-COO- +H3N-Tyr-Gly-Gly-Phe-Leu-COO￾Met-脑啡肽 Leu-脑啡肽 Cys Tyr ILe Gln Asn Cys Pro Leu Gly NH2 S S 牛催产素 Cys Tyr Gln Asn Cys Pro S S Phe Arg Gly NH2 牛加压素