Phenylalanine

Eight amino acids including tyrosine, tryptophan, threonine, glutamic acid, aspartic acid, histidine, phenylalanine, and arginine (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) were added into a 30% methanol aqueous solution of azalomycin F (100 μM) to obtain a mixed solution by vortexing, according to the molar concentration ratio of azalomycin F to each amino acid of 1:8. Simultaneously, the 30% methanol aqueous solution that only contained 100 μM azalomycin F was prepared as a blank control for background subtraction. After being incubated in a water bath at 37 °C for 30 min, these solutions were analyzed by a TripTOF 5600+ mass spectrometry (AB Sciex, Framingham, MA, USA) with an electrospray ion resource, and the detailed parameters are shown in Table S3 for negative ionization modes.

Sea cucumber (Acaudina molpadioidea) was purchased from a local market (Qingdao, China) and its water content was determined to be 12.65% per 20 g on average. Hippuryl histidyl leucine (HHL), rabbit-lung ACE and Sephadex G-15 were purchased from Sigma Chemical Ltd (St. Louis, MO, USA). Papain (from papaya) and trypsin (from bovine sources) were purchased from Nanning Pangbo Biological Engineering Ltd (Nanning, China). O-Pthaldialdehyde (OPA) was purchased from Beijing Soularbio Technology Ltd. (Beijing, China). Proline (PubChem CID 145742), valine (PubChem CID 6287), tyrosine (PubChem CID 6057), tryptophan (PubChem CID 6305), leucine (PubChem CID 6106) and phenylalanine (PubChem CID 6140) were purchased from Sinopharm Chemical Reagent Ltd. (Shanghai, China). All other chemicals were obtained from local commercial sources and were of the highest purity available.