Properties of a complex of Fe(III)-soybean lipoxygenase-1 and 4-nitrocatechol.
Fe(III)-soybean lipoxygenase-1 yields with 4-nitrocatechol a green coloured 1 : 1 complex, which shows at pH 7.0 absorption maxima at 385 nm and 650 nm. The formation of this complex is reversible. The circular dichroism spectrum of the complex of Fe(III)-lipoxygenase-1 and 4-nitrocatechol has a positive band at around 380 nm and a negative band at around 450 nm and is significantly different from that of the Fe(III)-enzyme as such. 4-Nitrocatechol can be displaced from the green complex by 13-L-hydroperoxy-cis-9, trans-11-octadecadienoic acid, resulting in the formation of the blue complex between the Fe(III)-enzyme and 13-L-hydroperoxy-cis-9,trans-11-octadecadienoic acid both under aerobic and anaerobic conditions. Also linoleic acid competes with 4-nitrocatechol for the binding site on the Fe(III)-enzyme, as can be demonstrated under anaerobic conditions, ultimately leading to reduction of the Fe(III)-enzyme. The oxygenation of linoleic acid by Fe(III)-lipoxygenase-1 is inhibited by 4-nitrocatechol. From steady-state kinetics a non-competitive inhibition pattern is obtained. Probably it has to be considered as pseudo non-competitive because of the slow establishment of the complex equilibrium. An inhibition constant (K4NC) of 16.3 microM is found. On prolonged incubation of Fe(III)-lipoxygenase-1 and 4-nitrocatechol the green complex converts into a brown species. This conversion is found to be coupled with a change in the nature of the inhibition from reversible to irreversible. A complex between native lipoxygenase-1 and 4-nitrocatechol is found to be unlikely.
D002396:Catechols / Q000032:analysis*; D002942:Circular Dichroism; D005290:Ferric Compounds / Q000032:analysis* / Q000378:metabolism; D007501:Iron / Q000032:analysis*; D007700:Kinetics; D008041:Linoleic Acids / Q000378:metabolism; D008084:Lipoxygenase / Q000032:analysis* / Q000378:metabolism; D008968:Molecular Conformation; D009574:Nitro Compounds / Q000032:analysis / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D013025:Glycine max; D013057:Spectrum Analysis
D002396:Catechols; D005290:Ferric Compounds; D008041:Linoleic Acids; D009574:Nitro Compounds; D007501:Iron; D008084:Lipoxygenase; C001833:4-nitrocatechol