Fig. 1

Graphic display of the currently known VC synthesis pathways. The final oxidation step of the distinct aldono-1,4-lactone to ascorbate is performed by a FAD-linked oxidase or dehydrogenase (GULO or GALDH). Photosynthetic protists appear to possess enzymatic components from animal and plant pathways, and due to this characteristic, the current described pathway for these species likely evolved from a secondary endosymbiosis event regarding a non-photosynthetic ancestor and algae [15]. The figure here presented and the corresponding description were adapted from the literature [14]