Vitamin B5 (pantothenate) and CoA biosynthesis Pathway (Zea mays)

Jump to: navigation, search

Pantothenate is the precursor of coenzyme A (CoA), the acyl carrier in scores of reactions. Pantothenate is made in the cytosol from pantoate and β-alanine, then converted to CoA in five steps, all probably cytosolic (Webb and Smith, 2011); the fifth step may also occur in plastids and peroxisomes. The three-step pathway to pantoate is not fully defined, but it is clear that step two, conversion of α-keto-isovalerate to ketopantoate, is mitochondrial (Ottenhof et al., 2004). Step one, α-keto-isovalerate formation from valine, is thus likely catalyzed by a mitochondrial branched chain aminotransferase (Taylor et al., 2004). The enzyme for step three (ketopantoate reduction to pantoate) is not known, so it is unclear whether this step is located in mitochondria or the cytosol. The details of the pantothenate and CoA biosynthesis (especially their compartmentalization) in plants are far from being elucidated. This diagram is an attempt to capture the current state of the field