Messenger RNA from isolated aleurone cells directs the synthesis of an alpha-galactosidase found in the endosperm during germination of guar (Cyamopsis tetragonaloba) seed.

In cereals and some legumes the aleurone layer is a site of synthesis of enzymes which mobilize endosperm reserves. It has been established whether or not the aleurone cells of the seed endosperm of Cyamopsis tetragonaloba are a site of synthesis of α-galactosidase. The isolation and cultivation of aleurone cells demonstrated that they contain mRNA which directs the synthesis and secretion of α-galactosidase into the endosperm where along with a ß-mannanase it is responsible for the degradation of the galactomannan storage polymer. A method was developed to purify the mRNA from the aleurone cells of germinating seeds. This mRNA was analysed by: i) Northern blot hybridization using oligo-nucleotide mixed probes derived from the protein's NH2-terminal amino acid sequence and ii) in vitro translation in a wheat germ system and detection of the α-galactosidase protein using antibodies. The molecular mass of the protein synthesized in vitro is slightly larger (44 kDa) than that of the mature α-galactosidase (40.5 kDa) which is as expected for the precursor of a secreted protein.

Stereoselective oxidation of styrene to styrene oxide in rats as measured by mercapturic acid excretion.

1. Administration of styrene (I) and styrene oxide (II) to rats resulted in the excretion of 2-hydroxymercapturic acids, N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (III) and N-acetyl-S-(2-phenyl-2-hydrosyethyl)cysteine (IV). Each appeared to be a mixture of diastereoisomers. 2. Administration of optically pure styrene oxide resulted in formation of one set of diastereoisomers. Racemic styrene oxide gave equal amounts of diastereoisomers. Thus the opening of the epoxide ring by glutathione S-transferases was stereospecific and the transferases showed no preference for one of the isomers of styrene oxide. 3. After administration of styrene the observed ratio of the diastereoisomers for both hydroxymercapturic acids was about 1:4. This leads to the conclusion that there is a stereoselective oxidation of styrene to styrene oxide, with a preference for the R-isomer.

Phenaceturic acid, a new urinary metabolite of styrene in the rat.

1. After administration of styrene to rat, phenaceturic acid, a new metabolite, was isolated. After administration of d8-styrene to rat, deuterium-labelled phenaceturic acid was excreted in the urine. 2. Two metabolic pathways are proposed, based on mass spectra of the deuterium-labelled phenaceturic acid. 3. After a single dose of styrene (250 mg/kg), the excreted phenaceturic acid originating from styrene in the urine amounted to 1.4% dose.

Mechanism of formation of mercapturic acids from (1-bromoethyl)benzene and (2-bromoethyl)benzene in the rat.

1. Three hypotheses have been proposed for the mechanism of metabolism of alkylhalides to hydroxy-alkylmercapturic acids, two of which involve the intermediate step of dehydrohalogenation and formation of an epoxide. 2. After injection of (1-bromoethyl)benzene in rat, the only mercapturic acid appearing in the urine was N-acetyl-S-1-phenylethylcysteine. After injecting (2-bromoethyl)benzene in the rat only N-acetyl-S-2-phenylethylcysteine and N-acetyl-S-(2-phenyl-2-hydroxyethyl)cysteine were found in the urine. 3. Since the principal mercapturic acid formed from both styrene and styrene oxide could not be detected in the urine of rats receiving either 1- or 2-bromoethyl benzene, the intermediate formation of styrene or styrene oxide from the arylalkylhalides does not occur.

Identification of three sulphur-containing urinary metabolites of styrene in the rat.

1. After administration of styrene (1) to rat, three sulphur-containing urinary metabolites were isolated in the molar ratio of III : IV : V equal to 65 : 34 : 1. 2. These metabolites were identified as N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (III), N-acetyl-S-(2-phenyl-2-hydroxyethyl)cysteine (IV) and N-acetyl-S-(phenacyl)cysteine (V). 3. After a single dose (250 mg/kg, 2.4 mmol/kg) styrene, the totally excreted mercapturic acids in the urine amounted to 10.7 +/- 1.0% (n = 5) of the dose.