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. 2014 Dec 19;4(4):1050–1091. doi: 10.3390/life4041050

Figure 3.

Figure 3

Peptide cycle (aa1, aa2 = amino acids; Y = –OH or –NH-CHR-CO-Y; R, R’ = amino acid side chains; H = hydantoin ring; NCAA = N-carboxy-amino acid anhydride).