S U M M A R YNaphthalene oxygenase was induced in several pseudomonads when these were grown on salicylate as a carbon and energy source, or when salicylate was added to cultures growing on succinate. The enzyme was not induced in Pseudomonas strain ~c r~g 8 1 6when this was grown in the presence of catechol, although after the addition of this compound to cultures growing on succinate the levels of catechol I ,a-oxygenase and catechol a~-oxygenase were similar to those observed after the addition of salicylate. Furthermore, two structural analogues of salicylate, 2-aminobenzoic acid and 2-hydroxybenzyl alcohol, induced naphthalene oxygenase gratuitously. Therefore salicylate is probably the inducer of naphthalene oxygenase.
The oxidation of a number of thio ethers to Soxides (sulphoxidation) has been observed in biological systems. Compounds metabolized by mammals to the sulphoxide include chlorpromazine (Salzman & Brodie, 1956), 1,2-diphenyl-4-(phenylthioethyl)pyrazolidine-3,5-dione (Bums et al. 1957) and promazine (Walkenstein & Seifter, 1959). The oxidation occurs in microorganisms: (-)-biotin sulphoxide is produced by A8pergillu8 niger (Wright, Cresson, Valiant, Wolf & Folkers, 1954) and 17flacetoxy-7oc-methylthioandrost-4-en-3-one is converted by Catonectria decora into 17fi-hydroxy-7ctmethylsulphinylandrost-4-en-3-one (Holmlund et al. 1962). Several examples of the occurrence of sulphoxides in plants are known. They are principally S-alkyl-L-cysteine S-oxides, their derivatives and w-methylsulphinylalkyl isothiocyanate glucosides, and they have been reviewed recently by Virtanen (1962). The sulphoxidation of 4,4'-diaminodiphenyl sulphide has been observed in vitro with a preparation of guinea-pig-liver microsomes which required 1964
1. (+)-n-Propylmercapturic acid sulphoxide, i.e. (+)-N-acetyl-S-n-propyl-l-cysteine S-oxide, was prepared as the dicyclohexylammonium salt, (-)-n-propyl-mercapturic acid sulphoxide was prepared as the free acid, and S-isopropyl-l-cysteine and isopropylmercapturic acid were also prepared. 2. The metabolism of 1- and 2-bromopropane was studied by radiochromatographic examination of the urine excreted by rats that had been fed with a diet containing (35)S-labelled yeast and then injected subcutaneously with these compounds. In addition to n-propyl-mercapturic acid and 2-hydroxypropylmercapturic acid, the excretion of which has already been reported, n-propylmercapturic acid sulphoxide was shown to be a metabolite of 1-bromopropane. Sulphur-containing metabolites of 2-bromopropane, if present in the urine at all, were there in very small amounts. 3. n-Propylmercapturic acid and isopropylmercapturic acid were isolated from the urine of rats that had been injected subcutaneously with S-n-propyl-l-cysteine and S-isopropyl-l-cysteine respectively.
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