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. 2021 Jan 12;22(2):697. doi: 10.3390/ijms22020697

Figure 2.

Figure 2

Figure 2

Biosynthesis of 5-methoxytryptophan (5-MTP) and melatonin. (A) 5-MTP is produced in human fibroblasts, bone marrow mesenchymal stromal cells (BM-MSCs), vascular endothelial cells (ECs) and SMCs, bronchial and renal epithelial cells. Its synthesis is catalyzed by TPH-1 (tryptophan hydroxylase-1) followed by hydroxyindole O-methyltransferase (HIOMT, also known as N-acetylserotonin O-methyltransferase, ASMT). HIOMT298 denotes HIOMT isoform coding for 298 aa HIOMT. (B) For comparison, melatonin biosynthesis in pineal cells is shown, highlighting HIOMT345 (ASMT 345) as the functional isoform. (C) Structural comparison between 5-MTP and melatonin.