The cyclic tetrapyrrole heme is used as a prosthetic group in a broad variety of different proteins in almost all organisms. Often, it is essential for vital biochemical processes such as aerobic and anaerobic respiration as well as photosynthesis. In Nature, heme is made from the common tetrapyrrole precursor 5-aminolevulinic acid, and for a long time it was assumed that heme is biosynthesized by a single, common pathway in all organisms. However, although this is indeed the case in eukaryotes, heme biosynthesis is more diverse in the prokaryotic world, where two additional pathways exist. The final elucidation of the two ‘alternative’ heme biosynthesis routes operating in some bacteria and archaea was achieved within the last decade. This review summarizes the three different heme biosynthesis pathways with a special emphasis on the two ‘new’ prokaryotic routes.

在几乎所有生物体中，环状四吡咯血红素都被用作各种蛋白质中的辅基。通常，它对于重要的生化过程（如需氧和厌氧呼吸以及光合作用）至关重要。在自然界中，血红素是由常见的四吡咯前体5-氨基乙酰丙酸制成的，长期以来，人们一直认为血红素是在所有生物体中通过单一的通用途径生物合成的。然而，尽管在真核生物中确实如此，但血红素的生物合成在原核世界中更为多样，因为存在两个其他途径。在过去的十年中，最终阐明了在某些细菌和古细菌中起作用的两种“替代”血红素生物合成途径。