Figure 1.

The main and the alternative L-ascorbic acid biosynthetic pathways in higher plants. Reactions with question marks yet to be identified. 1, glucose-6-phosphate isomerase; 2, mannose-6-phosphate isomerase (PMI; EC; 3, phosphomannomutase (PMM; EC; 4, GDP-D-mannose pyrophosphorylase (VTC1 or GMP; EC; 5, GDP-D-mannose 3,5-epimerase (GME; EC; 6, GDP-L-galactose-phosphorylase (VTC2 or GGP; EC; 7, L-galactose-1-P phosphatase (VTC4 or GPP; EC; 8, L-galactose dehydrogenase (GalDH; EC; 9, L-galactono-1,4-lactone dehydrogenase (GLDH; EC; 10, nucleotide pyrophosphatase or sugar-1-P guanyltransferase; 11, sugar phosphatase; 12, sugar dehydrogenase; 13, L-gulono-1,4-lactone oxidase (EC; 14, D-galacturonate-1-phosphate uridyltransferase and D-galacturonate-1-phosphate phosphatase (possible); 15, D-galacturonate reductase (GalUR; EC 1.1.1.n9); 16, aldonolactonase; 17, myo-inositol oxygenase (MIOX; EC; 18, D-glucuronate reductase (EC; 19, L-gulonolactonase; 20, D-glucuronate-1-phosphate uridyltransferase; 21, D-glucurono-1-phosphate phosphatase.

Mellidou et al. BMC Plant Biology 2012 12:239   doi:10.1186/1471-2229-12-239
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