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It does not settle possible intact NMN transport in all tissues or identify a specific phosphatase.\nexposure: 10 micromolar labelled NMN, sampled over 24 h; reported seven-hour comparison\nevidence_span: {\"source_cache\": \"artifacts/niacin-precursors-sources/nmrk2016.paragraphs.txt\", \"locator\": \"Normalized full-text paragraphs 12–12 (0-based)\", \"start_char\": 12567, \"end_char\": 14130, \"file_sha256\": \"fcbd5465aff51c9870d65fc9812edbad2cdf2af8bb16b6afb3170d7f0503178a\", \"text_sha256\": \"69b7b09a26aadc957c5bcb7c3f38cd4a426b94162ce4ff5424e98fe679c4e47c\"}\nsupporting_evidence_spans: [{\"source_cache\": \"artifacts/niacin-precursors-sources/nmrk2016.paragraphs.txt\", \"locator\": \"Normalized full-text paragraphs 38–38 (0-based)\", \"start_char\": 39692, \"end_char\": 41308, \"file_sha256\": \"fcbd5465aff51c9870d65fc9812edbad2cdf2af8bb16b6afb3170d7f0503178a\", \"text_sha256\": \"06af8996de76dd8a158899f05c337e45aa341ac5bd340a12cd041c89bc4c2d13\"}]\n[b3-pre-nmrk2016] NRK1 controls nicotinamide mononucleotide and nicotinamide riboside metabolism in mammalian cells. 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