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T R Tephly

Publications and source records attributed to T R Tephly.

At least 91 records · Page 5Linked to original sources
PubMed1983

Separation, purification and characterization of three isoenzymes of UDP-glucuronyltransferase from rat liver microsomes.

Three isoenzymes of UDP-glucuronyltransferase (UDPGT) have been separated and purified from liver microsomes of untreated female rats or female rats pretreated with 3-methylcholanthrene. The UDPGT isoenzymes were purified utilizing Chromatofocusing, column isoelectric focusing, and UDP-hexanolamine Sepharose 4B affinity chromatography. UDPGT activities could also be separated during UDP-hexanolamine affinity chromatography by elution with different UDPGA (UDP-glucuronic acid) concentrations. One isoenzyme exhibits a subunit molecular weight of 56,000 and is capable of conjugating p-nitrophenol, 1-naphthol, and 4-methylumbelliferone. This isoenzyme is inducible by 3-methylcholanthrene treatment and requires high UDPGA concentrations for elution from the UDP-hexanolamine affinity column in contrast to the other UDPGT isoenzymes. A second isoenzyme was purified and displayed a subunit molecular weight of 50,000. This isoenzyme was not induced by 3-methylcholanthrene and was active towards testosterone, the 17-OH position of beta-estradiol, p-nitrophenol, and 1-naphthol. A third isoenzyme was also purified and exhibited a subunit molecular weight of 52,000. This isoenzyme conjugated androsterone and etiocholanolone and was not induced by 3-methylcholanthrene treatment. This study reports the purification of two separate and distinct rat liver UDPGT isoenzymes capable of conjugating p-nitrophenol, only one of which is inducible by 3-methylcholanthrene treatment. Also, this is the first report of the purification of a UDPGT isoenzyme active towards the 3-OH position of androgens.

Animals↗
PubMed1983

Methanol toxicity in the monkey: effects of nitrous oxide and methionine.

Methanol poisoning in monkeys and humans is characterized by the development of formic acidemia, metabolic acidosis and ocular toxicity. Formate, the metabolite associated with the toxicity of methanol, is oxidized to carbon dioxide by a tetrahydrofolate-dependent pathway. Nitrous oxide treatment was used to inhibit the tetrahydrofolate-generating enzyme, 5-methyltetrahydrofolate homocysteine methyltransferase (methionine synthetase, E.C. 2.1.1.13.), to delineate the role of this enzyme in regulating formate oxidation in the monkey. The importance of methionine in the regulation of formate oxidation in the monkey also was evaluated. Nitrous oxide inhibited the oxidation of formate generated from the metabolism of methanol (1 g/kg i.p.) in the monkey, resulting in the development of severe metabolic acidosis and high blood formate levels in these animals compared with air-breathing monkeys administered the same dose of methanol. Treatment of nitrous oxide-exposed monkeys with repetitive doses of methionine (100 mg/kg 10, 12 and 14 hr after methanol) reversed the effects of nitrous oxide on formate oxidation, resulting in a marked decrease in blood formate levels and an increase in the rate of [14C]O2 formation from methanol. Methionine treatment also reversed the development of metabolic acidosis and bicarbonate depletion observed in nitrous oxide-exposed monkeys. These results indicate that hepatic methionine synthetase is important in the regulation of tetrahydrofolate-dependent metabolism in the monkey and that the generation of tetrahydrofolate by this enzyme is a major factor in determining the sensitivity of a species to methanol poisoning.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1983

Effect of nitrous oxide and methionine treatments on hepatic S-adenosylmethionine and methylation reactions in the rat.

Nitrous oxide administration to experimental animals leads to significant alterations in the hepatic folate pathway. This pathway is closely linked to the metabolism of methionine and S-adenosylmethionine (AdoMet), two compounds that play a central role in biologically important methylation reactions. This study was carried out to assess whether nitrous oxide administration to animals can affect the metabolism of AdoMet and the AdoMet-dependent methylation reactions. Exposure of rats to a mixture of nitrous oxide and oxygen (50:50) for 2 hr reduced hepatic AdoMet levels. However, when methionine was administered to these rats, hepatic AdoMet rapidly increased to levels that were significantly higher than those observed in air-exposed animals. Concomitant with this increase, there was a significant and marked increase in the rate of methylation of phospholipids and carboxymethylation of proteins. Thus, nitrous oxide, in addition to its inhibitory effect on 5-methyltetrahydrofolate:homocysteine methyltransferase (methionine synthase, EC 2.1.1.13) activity, possesses another effect. It increases the rate of conversion of exogenously administered methionine into AdoMet with a subsequent increase in the rate of methylation of key cellular constituents.

Animals↗
PubMed1982

Heme biosynthesis in the heart.

The rates of biosynthesis of heme a and heme b in hearts of fed and fasted rats were measured using an isolated heart perfusion system. delta-Aminolevulinic acid synthetase activity was decreased in hearts of fasted rats to about 30% of values in hearts obtained from fed rats. [14C] Glycine incorporation into hemes a and b of cardiac tissue obtained from fasted rats was also decreased to about 30% of values obtained in hearts from fed rats. Cobalt addition to the perfusion fluid led to a decrease in cardiac delta-aminolevulinic acid synthetase activity just as cobalt administration to rats does in vivo. These studies strongly suggest that delta-aminolevulinic acid synthetase activity regulates the rate of synthesis of hemes a and b in the heart.

5-Aminolevulinate Synthetase↗
PubMed1981

Blood methanol concentrations in normal adult subjects administered abuse doses of aspartame.

Blood methanol concentrations were measured in 30 normal adult subjects administered aspartame, a dipeptide methyl ester. The doses studied included the 99th percentile of projected daily ingestion (34 mg/kg body weight) and three doses considered to be in the abuse range (100, 150, and 200 mg/kg body weight). Methanol concentrations were below the level of detection (0.4 mg/dl) in the blood of the 12 normal subjects who ingested aspartame at 34 mg/kg. They were significantly elevated (p less than or equal to 0 .001) after ingestion of each abuse dose, with the mean peak blood methanol concentrations and the areas under the blood methanol concentration-time curve increasing in proportion to dose. Mean (+/- SD) peak blood methanol concentrations were 1.27 +/- 0.48 mg/dl at the 100 mg/kg dose, 2.14 +/- 0.35 mg/dl at the 150 mg/kg dose, and 2.58 +/- 0.78 mg/dl at the 200 mg/kg dose. Blood methanol concentrations returned to predosing levels by 8 h after administration of the 100 mg/kg dose. Methanol was still detected in the blood 8 h after the subjects had ingested aspartame at 150 or 200 mg/kg. Blood formate analyses were carried out in the 6 subjects who ingested aspartame at 200 mg/kg, since recent studies indicate that the toxic effects of methanol are due to formate accumulation. No significant increase in blood formate concentrations over predosing concentrations was noted. No changes were noted in any of the blood chemistry profile parameters measured 24 h after aspartame ingestion, compared to values noted before administration. Similarly, no differences were noted in ophthalmologic examinations carried out before and after aspartame loading.

Adult↗
PubMed1981

Methanol poisoning and formate oxidation in nitrous oxide-treated rats.

Formic acid does not accumulate in the rat after the administration of methanol as it does in methanol-poisoned humans and monkeys. In addition, rats do not manifest the metabolic acidosis and ocular toxicity characteristic of methanol intoxication in primates. Nitrous oxide treatment was used to inhibit 5-methyltetrahydrofolate homocysteine methyltransferase (methionine synthetase, EC 4.2.99.10) in order to delineate the role of this enzyme in regulating the metabolism of formate in rats and in determining the sensitivity of this species to methanol intoxication. Nitrous oxide treatment resulted in a decrease in hepatic levels of nonmethylated tetrahydrofolate forms and an increase in 5-methyltetrahydrofolate. Rats treated with nitrous oxide exhibited a marked decrease in the rate of oxidation of formate to carbon dioxide. The rate of disappearance of formate from the blood in these animals was decreased to half the control rate. Rats treated with nitrous oxide and administered methanol accumulated formate in blood and developed metabolic acidosis. These studies support the concept of a key role of methionine synthetase in supplying the tetrahydrofolate required for the folate-dependent oxidation of formate to carbon dioxide as well as the importance of this pathway in determining the sensitivity of a species to methanol poisoning.

Amitrole↗