AKR4A and AKR4B families of aldo-keto reductase (AKR)
The AKR4A family of AKR includes Glycine max NAD(P)H-dependent 6'-deoxychalcone synthase (6DCS, EC 3.1.170), chalcone reductase (CHR, EC 2.3.1.74) from Medicago sativa, Glycyrrhiza echinate, and Glycyrrhiza glabra, which are founding members of aldo-keto reductase family 4 member A1 (AKR4A1), A2 (AKR4A2), A3 (AKR4A3), and A4 (AKR4A4), respectively. NAD(P)H-6DCS co-acts with chalcone synthase in formation of 4,2',4'-trihydroxychalcone, involved in the biosynthesis of glyceollin type phytoalexins. CHR, also called chalcone polyketide reductase, is a key enzyme of the flavonoid/isoflavonoid biosynthesis pathway. The AKR4B family of AKR includes Sesbania rostrate chalcone reductase (CHR, AKR4B1), Papaver somniferum codeinone reductase (COR, AKR4B2/ AKR4B3), Fragaria x ananassa D-galacturonate reductase (GalUR, AKR4B4), deoxymugineic acid synthase 1 (DMAS1) from Zea mays (AKR4B5), Oryza sativa (AKR4B6), Hordeum vulgare (AKR4B7), Triticum aestivum (AKR4B8), and Erythroxylum coca methylecgonone reductase (MecgoR, AKR4B10). CHR, also called chalcone polyketide reductase, is a key enzyme of the flavonoid/isoflavonoid biosynthesis pathway. NADPH-dependent COR and non-functional NADPH-dependent COR from Papaver somniferum are founding members of aldo-keto reductase family 4 member B2 (AKR4B2) and B3 (AKR4B3), respectively. NADPH-dependent COR (EC 1.1.1.247) reduces codeinone to codeine in the penultimate step in morphine biosynthesis. It can use morphinone, hydrocodone, and hydromorphone as substrates during reductive reaction with NADPH as cofactor, and morphine and dihydrocodeine as substrates during oxidative reaction with NADP as cofactor. GalUR (EC 1.1.1.365), also called aldo-keto reductase 2 (AKR2), is involved in ascorbic acid (vitamin C) biosynthesis by catalyzing the conversion from L-galactonate and NADP(+) to D-galacturonate and NADPH. DMAS1 (EC 1.1.1.285) catalyzes the reduction of a 3''-keto intermediate during the biosynthesis of 2'-deoxymugineic acid (DMA) from L-Met. It is involved in the formation of phytosiderophores (MAs) belonging to the mugineic acid family and required to acquire iron. MecgoR catalyzes the stereospecific reduction of methylecgonone to methylecgonine, the penultimate step in cocaine biosynthesis.
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