Arabidopsis alkenal double bond reductase and leukotriene B4 12-hydroxydehydrogenase
This group includes proteins identified as the Arabidopsis alkenal double bond reductase and leukotriene B4 12-hydroxydehydrogenase. The Arabidopsis enzyme, a member of the medium chain dehydrogenase/reductase family, catalyzes the reduction of 7-8-double bond of phenylpropanal substrates as a plant defense mechanism. Prostaglandins and related eicosanoids (lipid mediators involved in host defense and inflamation) are metabolized by the oxidation of the 15(S)-hydroxyl group of the NAD+-dependent (type I 15-PGDH) 15-prostaglandin dehydrogenase (15-PGDH) followed by reduction by NADPH/NADH-dependent (type II 15-PGDH) delta-13 15-prostaglandin reductase (13-PGR) to 15-keto-13,14,-dihydroprostaglandins. 13-PGR is a bifunctional enzyme, since it also has leukotriene B(4) 12-hydroxydehydrogenase activity. Leukotriene B4 (LTB4) can be metabolized by LTB4 20-hydroxylase in inflamatory cells, and in other cells by bifunctional LTB4 12-HD/PGR. These 15-PGDH and related enzymes are members of the medium chain dehydrogenase/reductase family. The medium chain dehydrogenases/reductase (MDR)/zinc-dependent alcohol dehydrogenase-like family, which contains the zinc-dependent alcohol dehydrogenase (ADH-Zn) and related proteins, is a diverse group of proteins related to the first identified member, class I mammalian ADH. MDRs display a broad range of activities and are distinguished from the smaller short chain dehydrogenases (~ 250 amino acids vs. the ~ 350 amino acids of the MDR). The MDR proteins have 2 domains: a C-terminal NAD(P) binding-Rossmann fold domain of an beta-alpha form and an N-terminal catalytic domain with distant homology to GroES.