Abstract
In recent years vitamin B6 has become a focus of research describing the compound’s critical function in cellular metabolism and stress response. For many years the sole function of vitamin B6 was considered to be that of an enzymatic cofactor. However, recently it became clear that it is also a potent antioxidant that effectively quenches reactive oxygen species and is thus of high importance for cellular well-being. In view of the recent findings, the current review takes a look back and summarizes the discovery of vitamin B6 and the elucidation of its structure and biosynthetic pathways. It provides a detailed overview on vitamin B6 both as a cofactor and a protective compound. Besides these general characteristics of the vitamin, the review also outlines the current literature on vitamin B6 derivatives and elaborates on recent findings that provide new insights into transport and catabolism of the compound and on its impact on human health.
Highlights
The Discovery of Vitamin B6The formula of vitamin B6 was first published by Ohdake in 1932.He worked on the isolation from rice-polishings of what he called “Oryzanin” (Vitamin B1) and found vitB6 as a by-product [1, 2]
The second known de novo vitB6 biosynthesis pathway is the deoxyxylose 5’phosphate (DXP)-independent pathway, which is found in bacteria, archaea, and eukarya [13, 33, 34]
The occurrence of this pathway is demonstrated in plants, fungi, Plasmodium falciparum, Thermotoga maritima as well as Bacillus subtilis and involves two proteins, PDX1 and PDX2
Summary
The formula of vitamin B6 ( referred to as vitB6) was first published by Ohdake in 1932. It was shown that in E. coli, vitB6 is synthesized by the action of PdxJ (EC 2.6.99.2) and PdxA (EC 1.1.1.262) (Figure 1) [23,24,25] These two vitB6 synthase proteins use 4-phospohydroxy-Lthreonine (4HPT) and DXP, which are precursors in isoprenoid and thiamine biosynthesis, respectively, as substrates to form PNP [26,27,28]. The second known de novo vitB6 biosynthesis pathway is the DXP-independent pathway, which is found in bacteria, archaea, and eukarya [13, 33, 34] The occurrence of this pathway is demonstrated in plants, fungi, Plasmodium falciparum, Thermotoga maritima as well as Bacillus subtilis and involves two proteins, PDX1 and PDX2 The core of the PLP synthase complex consists of 12 PDX1 enzymes that interact in two hexameric layers joining face-to-face to form a dodecamer onto which 12 PDX2 monomers attach [37, 39, 40]
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