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PubMed1989

Oxidative metabolism of 14C-pyridine by human and rat tissue subcellular fractions.

1. The oxidative metabolism of 14C-pyridine by human and rat microsomal fractions has been studied. Metabolites were separated by h.p.l.c. employing continuous radioactivity monitoring of the column effluent. 2. Human liver microsomal fractions incubated with an NADPH-generating system and oxygen formed pyridine N-oxide (PNO) at an average rate of 275 pmol/min per mg protein, 2-pyridone (2PO) at 207 pmol/min per mg and 4-pyridone (4PO) at 154 pmol/min per mg. One human subject formed 3-hydroxypyridine N-oxide in addition to the other metabolites. 3. Human kidney microsomal fractions formed PNO, 2PO and 4PO at rates similar to those with human liver microsomal fractions, whereas human lung microsomal fractions formed the metabolites at less than half the rate. 4. Metabolism of pyridine by human liver microsomal fractions was inhibited 54% by nitrogen, 34% by 80% carbon monoxide-20% oxygen, and 20% by metyrapone. 2-Diethylaminoethyl-2,2-diphenylvalerate HCl (SKF-525A) did not inhibit pyridine metabolism. 5. Liver microsomal fractions from non-induced rats metabolized pyridine to PNO at a rate of 19 pmol/min per mg protein, 2PO at 17 pmol/min per mg and 4PO at 61 pmol/min per mg. 6. There was no pyridine metabolism by human or rat tissue cytosolic fractions incubated under the same conditions.

Animals↗
PubMedDate not supplied

Metabolism of di-2-ethylhexyl phthalate by subcellular fractions from rainbow trout liver.

Trout liver homogenates metabolized di-2-ethylhexyl phthalate (DEHP) to monoethylhexyl phthalate (MEHP) without added NADPH and to MEHP and more polar metabolites with added NADPH. Both hydrolysis and oxidative metabolism of DEHP were inhibited by piperonyl butoxide. The 10,000g pellet, 100,000g pellet and 100,000g supernatant fraction from liver homogenates all catalyzed the hydrolysis of DEHP and all but the 100,000g supernatant fraction showed the shift to more polar metabolites with added NADPH; serum also catalyzed the hydrolysis of DEHP. Measurement of the microsomal marker, glucose 6-phosphatase, and the mitochondrial marker, succinic dehydrogenase, revealed that DEHP-hydrolytic activity was associated with microsomes and the 100,000g supernatant fraction, whereas DEHP oxidation was associated only with microsomes.

Animals↗
PubMed1980

Calcium exchangeability in subcellular fractions of pancreatic islet cells.

The distribution and exchangeability of calcium within subcellular compartments of rat pancreatic islet cells was determined in pulse-chase experiments following isotopic labelling with 45Ca2+. In unstimulated islets the mitochondrial fraction showed the greatest, and the insulin secretory granule fraction the least, uptake of 45Ca2+; subsequently the rate of loss from each compartment during 120 min was in the order mitochondrial greater than microsomal greater than secretory granule fraction. On exposure to D-glucose, 16.8 mM, the 45Ca labelling of all 3 subcellular compartments was increased after 5 and 30 min stimulation. In contrast, theophylline 10 mM caused a significant decrease in mitochondrial 45Ca content with little effect on other compartments. These results are discussed in relation to the importance of calcium disposition, exchangeability, and mobility for the initiation and control of insulin secretion.

Animals↗
PubMed1980

Distribution of 65Zn in mice with melanomas and in the subcellular fractions of melanomas.

The tissue distribution of injected 65Zn into mice with Harding--Passey or B-16 melanomas was studied. Both types of melanoma took up remarkably large amounts of 65Zn (harding--Passey 17.4%; and B-16 almost 26.0% of the 65Zn dose administered). In the case of the B-16 melanoma, the tumor was the dominant site of incorporation even in terms of specific activity. On a subcellular level, melanosomes isolated by gradient ultracentrifugation were shown to be sites of preferred deposition of 65Zn. The uptake of 65Zn by melanomas and its specific binding by melanomes suggests that this isotope might be useful in detecting melanomas.

Animals↗