4PYD:
reference: Mechanism of pyranopterin ring formation in molybdenum cofactor biosynthesis., Hover BM, Tonthat NK, Schumacher MA, Yokoyama K, Proc Natl Acad Sci U S A. 2015 May 19;112(20):6347-52. doi:, 10.1073/pnas.1500697112. Epub 2015 May 4. PMID: 25941396

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