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Phenolic products obtained on isomerization of the three arene oxides of toluene, the nine arene oxides of ortho-, meta-, and para-xylene, the arene oxide of mesitylene, and 2-methyl and 1,2-dimethylnaphthalene-1,2-oxides are compared to the phenolic products obtained by hepatic metabolism of the parent aromatic hydrocarbons. The results are compatible with the intermediacy of certain of these arene oxides in the metabolic pathway from hydrocarbons to phenols. Migrations of methyl groups as well as a remarkable apparent migration of oxygen are observed. The isomerization of 1,4-dimethylbenzene oxide to 2,4-dimethylphenol is analogous to the methyl migration observed in the enzymatic conversion of 4-methylphenylalanine to 3-methyltyrosine with phenylalanine hydroxylase. There are multiple pathways of isomerization of alkylarene oxides to phenols and they are determined by environmental and structural factors. The proportion and nature of products vary greatly with pH, which suggests the presence of different mechanisms for acid-catalyzed or spontaneous isomerizations of arene oxides.
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The properties of peroxisomal enzyme alkylglycerone-phosphate synthase were studied in highly purified peroxisome fractions of rat liver. The requirements for optimal enzyme activity: pH and composition of the reaction mixture, incubation time, and enzyme concentration were investigated, and kinetic studies performed employing both different long-chain fatty alcohols and acyl dihydroxyacetone phosphates as substrates. Activities of the synthase considerably higher as reported before were found in the peroxisome preparation, with alkylglycerone (alkyldihydroxyacetone) phosphate as the sole product of the exchange reaction. The kinetic studies revealed divergent properties of peroxisomal synthase with respect to the substrates involved. Whereas the substrate concentration versus reaction velocity plot for the fatty alcohols reflects Michaelis-Menten kinetic behavior, it displays a maximum followed by inhibition with regard to the acylglycerone phosphate. The enzyme accepts different acylglycerone phosphates without much specificity but it is most active with 9-cis-octadecenol.
Misincorporation of 2-hydroxyethylated amino acids into hemoglobin during de novo synthesis was studied by injecting mice with radiolabelled N-(2-hydroxyethyl)valine, S-(2-hydroxyethyl)cystine or N tau-(2-hydroxyethyl)histidine. The results showed that S-(2-hydroxyethyl)cysteine and N tau-(2-hydroxyethyl)histidine were misincorporated, whereas N-(2-hydroxyethyl)valine was not. Monitoring of in vivo doses of hydroxyethylating agents by determination of N-(2-hydroxyethyl)valine was free of the disturbing influence of such misincorporation.
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