Fig. 5.

Biosynthetic pathway of N-retinylidene-N-retinyl-glycerophosphoethanolamine (A2-GPE)

N-retinylidene-glycerophosphoethanolamine (NR-GPE) and dihydropyridinium A2-GPE, like N-retinylidene-phosphatidylethanolamine (NR-PE) and dihydropyridinium N-retinylidene-N-retinyl-phosphatidylethanolamine (A2PE) in the N-retinylidene-N-retinyl-ethanolamine (A2E) biosynthetic route, ought to play important roles in the biogenesis of A2-GPE. Due to the susceptibility of the dihydropyridinium ring to auto-oxidation, it is concluded that dihydropyridinium A2-GPE, like dihydropyridinium A2PE, is not found in the eye and biomimetic chemical reactions, from which NR-GPE is, however, possible to be trapped by high-performance liquid chromatography (HPLC)