An octaethylene glycol monododecyl ether-based mixed micellar assay for lipoxygenase acting at neutral pH

Biological studies of new organotin(IV) complexes of thioamide ligands

New organotin(IV) complexes with heterocyclic thioamides 2-mercapto-benzothiazole (Hmbzt), 5-chloro-2-mercapto-benzothiazole (Hcmbzt) and 2-mercapto-benzoxazole (Hmbzo) of formulae [(C(6)H(5))(3)Sn(mbzt)] (1), [(C(6)H(5))(3)Sn(cmbzt)] (3) and [(C(6)H(5))(2)Sn(cmbzt)(2)] (4), together with the already known [(C(6)H(5))(3)Sn(mbzo)] (2), [(n-C(4)H(9))(2)Sn(cmbzt)(2)] (5) and [(CH(3))(2)Sn(cmbzt)(2)] (6) were used to study their influence on the peroxidation of oleic acid. The influence of complexes (3)-(6) upon peroxidation of oleic acid showed that the formation of reactive radicals caused the initiation of the chain radical oxidation of the substrate. The influence of complexes (1)-(6) upon the catalytic peroxidation of linoleic acid by the enzyme lipoxygenase (LOX) was also studied and compared to those of cisplatin. Compounds (1)-(6) were finally tested for in vitro cytotoxicity against leiomyosarcoma cells.

Enhanced production of hydroperoxides by immobilized lipoxygenase in the presence of cyclodextrins

The advantages of the presence of cyclodextrins in a reaction catalyzed by immobilized lipoxygenase at neutral pH are reported for the first time. The steady-state rate in the presence of beta-cyclodextrins was seven times higher than in control experiments using the same concentration of linoleic acid; furthermore the percentage of substrate conversion (and product accumulation) obtained in the presence of beta-cyclodextrins was higher than in the control assays. The optimum concentration of free linoleic acid coincided with the critical micellar concentration for linoleic acid at neutral pH. The operational stability of the immobilized enzyme increased in the presence of beta-cyclodextins, while an increase in the percentage of 13-HPOD was also observed.

An octaethylene glycol monododecyl ether-based mixed micellar assay for determining the lipid acyl hydrolase activity of patatin

Patatin was extracted from potato tubers (Solanum tuberosum L. cv. Spunta) and purified to homogeneity by ammonium sulfate salt fractionation and one sole chromatographic step. A spectrophotometric mixed micellar assay for patatin lipid acyl hydrolase (LAH) activity was designed with the detergent octaethylene glycol monododecyl ether (C12E8). Patatin LAH used p-nitrophenyl butyrate (PNP-butyrate) as substrate when solubilized in (C12E8) micelles. In the mixed micellar system, patatin LAH responds to the PNP-butyrate surface concentration expressed as mol% (= [PNP-butyratel x 100/([detergentl critical micellar concentration)) and not to the molarity of PNP-butyrate. The kinetic parameters were determined; Vmax was independent of the mixed micelle concentration, as was Km, when expressed as mol%. However, Km was dependent on C12E8 concentration when expressed in molar concentration. C12E8/PNP-butyrate proved to be a reliable system for assaying patatin LAH activity and is superior to the commonly used Triton X-100 and SDS methods. It permits investigation of the substrate requirements of patatin LAH activity because the concentration-independent Km can be determined both in mol% and as the absolute number of substrate molecules per micelle. In addition, the detergent did not affect the enzyme activity.

Enzyme-catalyzed and enzyme-triggered pathways in dioxygenation of 1-monolinoleoyl-rac-glycerol by potato tuber lipoxygenase

It was shown for the first time that potato tuber lipoxygenase (ptLOX) catalyzed the aerobic oxidation of 1-monolinoleoyl-rac-glycerol (mLG) in a mixed micellar reaction solution with the non-ionic detergent monododecyl ether of decaoxyethylene glycol. No hydrolysis of mLG occurred during the reaction. The four major reaction products obtained at 23 degrees C were identified as 1-[9-hydroperoxy-10E,12Z-octadecadienoyl]-rac-glycerol (9-(E,Z)HPODE-GE, 41%), 1-[13-hydroperoxy-9Z,11E-octadecadienoyl]-rac-glycerol (13-(Z,E)-HPODE-GE, 17%), and their all-trans isomers ( approximately 21% each). The molar fraction of all-trans isomers depended on the temperature of the reaction solution; it was found that at 0 degrees C their molar fractions were approximately 15.5% each, while 9-(E,Z)HPODE-GE and 13-(Z,E)-HPODE-GE gave 42% and 27%, respectively, of the overall product. A free radical scavenger, 4-hydroxy-TEMPO, dramatically increased the molar fraction of 9-(E,Z)HPODE-GE, yielding 83% at 23 degrees C, at the expense of all other products. Chiral HPLC of 9-(E,Z)HPODE-GE formed in the presence of 4-hydroxy-TEMPO revealed that it was composed of approximately 94% S and approximately 6% (R) isomers. This assures largely a uniform orientation of mLG molecules in the ptLOX active center, with their methyl end most likely deepened into the protein globule. The second major product, 13-(Z,E)-HPODE-GE, which yielded approximately 9% of the total product formed in the presence of 4-hydroxy-TEMPO, was racemic, and so were the all-trans isomers. Therefore, the last three cannot be considered the true products of the enzyme reaction, which is known to be stereospecific. It appears that they were formed as a result of (i) leakage of the pentadienyl radicals from the ptLOX active center and their subsequent non-enzymatic dioxygenation, and/or (ii) leakage of the peroxyl radicals leading to a free radical chain reaction affording all positional, geometrical and stereoisomers of the products. This reaction resembles ptLOX oxidation of another non-ionizable substrate, linoleyl alcohol [I.A. Butovich, S.M. Luk'yanova, C.C. Reddy, Arch. Biochem. Biophys. 378 (2000) 65-77], and differed substantially from oxidation of ionizable linoleic acid. Consequently, formation of large amounts of the non-specific oxidation products might be considered a universal characteristic of ptLOX oxidation of non-ionizable compounds.