Figure 1

Retinoid biosynthesis. The conversion of β-carotene to retinoids, including retinal, retinol, retinoic acid, and retinyl esters (A). Biosynthesis of retinal in Escherichia coli using the MEP pathway and the exogenous MVA pathway (B). The gene names and the encoded enzymes are as follows: atoB/phaA, acetoacetyl-CoA synthase; mvaS, HMG-CoA synthase; mvaA, HMG-CoA reductase; mvaK1, mevalonate kinase; mvaK2, phosphomevalonate kinase; mvaD, mevalonate-5-diphosphate decarboxylase; idi, IPP isomerase; dxs, DXP synthase; ispA, FPP synthase; crtE, GGPP synthase; crtB, phytoene synthase; crtI, phytoene desaturase; crtY, lycopene cyclase; BCM(D)O, β-carotene 15,15'-mono- or dioxygenase. Pathway intermediates are as follows: G3P, D-glyceraldehyde-3-phosphate; DXP, 1-deoxy-D-xyluose-5-phosphate; MEP, 2-C-methyl-D-erythritol-4-phosphate; IPP, isopentenyl diphosphate; FPP, farnesyl diphosphate; GGPP, geranylgeranyl diphosphate.