No abstract

Efforts have been made to characterize the products that result from interactions between Lhistidine (free base) and peroxidizing methyl linoleate (ML) in a model system consisting of reactants dispersed on a filter paper, lmidazole lactic acid and imidazole acetic acid are identified as breakdown products when histidine is incubated with ML, methyl linoleate hydroperoxide (MLHPO), or n-hexanal over a period of 3 weeks. Two other reaction products are found to give back histidine upon acid hydrolysis. These products are though to be Schiff's base compounds which result from the condensation of the histidyl a-amino group and carbonyl groups of reactive aldehydes formed during ML peroxidation. Most of the detectable reaction products have the imidazole moiety intact indicating the high relative reactivity of the functional groups, especially the amino group, associated with the a-carbon. Such high reactivity provides an explanation for the low concentrations of ninhydrin-positive free amino compounds that are, at best, barely detectable on thin layer chromatography.

No abstract

As a part of our study on the interactions between peroxidizing lipids and the histidyl imidazole side-chain in simple, low-moisture model systems, 4-methylimidazole (4MI) was reacted with methyl linoleate (ML). This analogue was chosen to avoid interference from other functional groups in histidine (free base) or in proteins. Changes in the concentrations of lipid hydroperoxides, carbonyls, 4MI, and brown pigments were followed over a period of 24 days. The results indicate that 4MI exhibits significant prooxidative activity by reducing the induction period as well as by enhancing the formation of brown pigments. These effects are more pronounced at high 4MI/MI molar ratios and under basic pH's. Upon interactions with peroxidizing ML, as much as 44% of initially present 4MI was destroyed by the sixth day of incubation.

Safflower oil, methyl oleate, and methyl linoleate were oxidized in a closed system where they were in contact with vapor space over previously oxidized methyl linoleate. The volatile compounds resulting from linoleate oxidation greatly accelerated peroxidation of the oil and the two esters. Similar results were obtained when safflower oil and methyl esters of oleic acid and linoleic acid were contacted with vapor phase over hexanal or 2,3‐decadienal, both of which are major products of decomposition of peroxides formed from peroxidized linoleate.