Vitamin B₁₂, cobalamin, is a cobalt-containing ring-contracted modified tetrapyrrole that represents one of the most complex small molecules made by nature. In prokaryotes it is utilised as a cofactor, coenzyme, light sensor and gene regulator yet has a restricted role in assisting only two enzymes within specific eukaryotes including mammals. This deployment disparity is reflected in another unique attribute of vitamin B₁₂ in that its biosynthesis is limited to only certain prokaryotes, with synthesisers pivotal in establishing mutualistic microbial communities. The core component of cobalamin is the corrin macrocycle that acts as the main ligand for the cobalt. Within this review we investigate why cobalt is paired specifically with the corrin ring, how cobalt is inserted during the biosynthetic process, how cobalt is made available within the cell and explore the cellular control of cobalt and cobalamin levels. The partitioning of cobalt for cobalamin biosynthesis exemplifies how cells assist metalation.

维生素 B ₁₂钴胺素是一种含钴环缩改性四吡咯，是自然界最复杂的小分子之一。在原核生物中，它被用作辅因子、辅酶、光传感器和基因调节剂，但在协助包括哺乳动物在内的特定真核生物中仅发挥两种酶的作用有限。这种部署差异反映在维生素 B ₁₂的另一个独特属性上，即其生物合成仅限于某些原核生物，而合成器对于建立互惠微生物群落至关重要。钴胺素的核心成分是corrin大环，它是钴的主要配体。在这篇综述中，我们研究了为什么钴与咕啉环特异性配对、钴如何在生物合成过程中插入、钴如何在细胞内提供，并探索钴和钴胺素水平的细胞控制。钴胺素生物合成中钴的分配例证了细胞如何协助金属化。