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. 2018 Sep 21;8:14228. doi: 10.1038/s41598-018-32591-z

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© The Author(s) 2018

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Heme-dependent feedback inhibition of ALAS in the heme biosynthetic pathway. (A) In the mammal cells, heme primarily regulates ALAS1 by inhibiting its mRNA expression and translation and by blocking the translocation of ALAS1 precursor protein into the mitochondria. Heme promotes the degradation of ALAS1 protein in mitochondria. (B) The heme biosynthesis in C. crescentus is negatively regulated via inactivation of cALAS by direct heme binding, where the excess free heme directly binds to each subunit of cALAS homodimer in one-to-one stoichiometry to releases an essential coenzyme PLP and is inactivated quickly, thus providing a mechanism for bacteria to react to the toxic unbound tetrapyrrole products. Abbreviations: PBG; porphobilinogen, HMB; hydroxymethylbilane, URO III; uroporphyrinogen III, CPP III; coproporphyrinogen III, CPPIX; coproporphyrinogen IX, PPIX; protoporphyrinogen IX, PBGS; porphobilinogen synthase, PBGD; porphobilinogen deaminase, UROS; uroporphyrinogen III synthase, UROD; uroporphyrinogen III decarboxylase, CPO; coproporphyrinogen III oxidase, PPO; protoporphyrinogen IX oxidase, FECH; ferrochelatase.