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E Niki

Publications and source records attributed to E Niki.

117 records · Page 7Linked to original sources
PubMed1984

Oxidation of lipids. 7. Oxidation of phosphatidylcholines in homogeneous solution and in water dispersion.

The rates and products of the oxidations of phosphatidylcholines (PCs) in organic homogeneous solutions and as multilamellar liposomes in an aqueous dispersion were studied at 50 degrees C initiated by oil-soluble and water-soluble azo compounds and with the aim primarily of elucidating the effect of substrate and the reaction medium. Polyunsaturated fatty acids were oxidized exclusively among the fatty acids in PC. The product distribution was determined by the number of double bonds: in the oxidation of methyl linoleate and dilinoleoyl PC, the conjugated diene hydroperoxides were formed almost quantitatively, whereas in the oxidation of PC and polyunsaturated fatty acids having three or more double-bonds, cyclic peroxides were also formed. The oxidizability of PC was dependent on the content of doubly allylic hydrogens and their reactivities were suggested to be similar, independent of parent substrate and reaction medium, although the oxidizability of PC in nonpolar organic solvents is markedly enhanced by the formation of reverse-phase micelles.

Animals↗
PubMed1984

Inhibition of oxidation of methyl linoleate in solution by vitamin E and vitamin C.

The oxidation of methyl linoleate in solution initiated with azo compounds has been studied in the absence and presence of vitamin E and vitamin C. Both vitamin E and vitamin C acted as a chain-breaking antioxidant and they suppressed the oxidation and produced an induction period. The inhibition rate constant for the scavenging of peroxy radical was calculated at 37 degrees C as kinh = 5.1 X 10(5) M-1 s-1 and 7.5 X 10(4) M-1 s-1 for vitamin E and vitamin C, respectively. It was suggested that each vitamin E could trap two peroxy radicals, whereas vitamin C could trap only one peroxy radical under the reaction conditions employed in this study. When both vitamin E and vitamin C were present, the oxidation was suppressed quite efficiently and the apparent inhibition rate constant was obtained as kinh = 4.0 X 10(5) M-1 s-1. Furthermore, vitamin E remained almost unchanged and only vitamin C was consumed at the initial stage and vitamin E was consumed after vitamin C was exhausted. It was concluded that vitamin E trapped the peroxy radical and the resulting alpha-chromanoxy radical reacted with vitamin C to regenerate vitamin E.

Ascorbic Acid↗
PubMed1976

Effect of clomiphene citrate on PMSG-induced ovulation in the immature rat.

The dose of 15 IU PMSG was found to be optimal for inducing ovulation within 74 hours in 27-day-old immature female rats. There was a significant decrease in the mean number of ova per ovulating animal when the dose was raised beyond this (r = 0.6554, p less than 0.001 for the range from 15 to 100 IU), but the number of ovulating animals did not decrease unless more than 80 IU PMSG were injected. The PMSG-induced ovulation was not affected by treating the animals with 10 or 100 mug clomiphene citrate at 0, 24, 48, 54, 60, 66 hours or at 0, 24, and 48 hours.

Age Factors↗
PubMedDate not supplied

Antioxidants in relation to lipid peroxidation.

The role of antioxidants in lipid peroxidation is reviewed. Specifically, the rate and mechanism of inhibition of lipid peroxidation by water-soluble and lipid-soluble, chain-breaking antioxidants have been discussed.

Antioxidants↗
PubMedDate not supplied

Characterization of imidazopyrroloquinoline compounds synthesized from coenzyme PQQ and various amino acids.

Imidazopyrroloquinoline (IPQ) compounds synthesized from coenzyme PQQ (pyrroloquinoline quinone) and various kinds of amino acids were characterized. IPQ was synthesized from coenzyme PQQ and one of three amino acids (glycine, L-tryptophan and L-tyrosine). Two kinds of IPQ compound were formed from coenzyme PQQ and L-serine. At higher pH, IPQ was synthesized, at lower pH hydroxy-methyl-IPQ was synthesized. IPQ with R of amino acids represented by R-CH(NH2)-COOH was synthesized from coenzyme PQQ and other amino acids. IPQ compounds do not act as cofactor of glucose dehydrogenase. Molar absorption coefficients of IPQ are 31,400 M-1 cm-1 at 251 nm, 30,700 M-1 cm-1 at 276 nm, and 20,700 M-1 cm-1 at 423 nm at pH 7.0 and room temperature.

Amino Acids↗
PubMedDate not supplied

Synthesis of esters of coenzyme PQQ and IPQ, and stimulation of nerve growth factor production.

Esters of pyrroloquinoline quinone (PQQ), a cofactor of microbial quinoprotein enzyme, and imidazopyrroloquinoline (IPQ, from PQQ and glycine) were synthesized, and their chemical stability, toxicity to L-M cells and nerve growth factor (NGF) inducing activity in L-M cells were studied. PQQ esters were found to be potent enhancers of NGF production, but IPQ esters had only marginal effects on NGF production. The monoester of PQQ with a methoxycarbonyl group at C-2 of PQQ is a most effective compound because of its NGF inducing activity, limited toxicity, safety and chemical stability. These results suggest that PQQ-2-esters could be developed as a curative or preventive drug for retrograde neural diseases in the central and perpheral nervous system.

Animals↗