Search PubMed⌕ Search

Biomedical subjects

N Nelson

Publications and source records attributed to N Nelson.

At least 253 records · Page 14Linked to original sources
PubMed1980

Cytoplasmically made subunits of yeast mitochondrial F1-ATPase and cytochrome c oxidase are synthesized as individual precursors, not as polyproteins.

At least three subunits of yeast mitochondrial F1-ATPase (ATP phosphohydrolase, EC 3.6.1.3) and at least two subunits of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) are synthesized outside the mitochondria and imported into the organelles as individual precursors that are between 2000 and 6000 daltons larger than the mature subunits. These precursors were shown to be primary translation products. Therefore, neither the five F1 subunits nor the four small cytochrome c oxidase subunits are synthesized as a single polyprotein.

Adenosine Triphosphatases↗
PubMed1980

Inhalation carcinogenicity of epichlorohydrin in noninbred Sprague-Dawley rats.

Inhalation exposure experiments with the direct-acting alkylating agent epichlorohydrin (ECH) were done on noninbred male Sprague-Dawley rats. Single 6-hour exposure to ECH and follow-up for 14 days showed the median lethal concentration to be about 360 ppm. Further inhalation experiments were done with 6-hour exposure 5 days/week. A short-term 30-exposure regimen with 100 ppm ECH produced malignant squamous cell carcinomas of the nasal cavity in 15 of 140 rats and respiratory tract papillomas in 3 rats. Among 100 rats, lifetime exposure to 30 ppm yielded 1 malignant squamous carcinoma of the nasal cavity plus 1 nasal papilloma. No nasal or respiratory tract tumors were produced by lifetime exposure of 100 rats to 10 ppm. As controls, 100 air-treated and 50 untreated rats were used. A dose-rate effect was observed for ECH inasmuch as 30-day exposure to 100 ppm (3,000 ppm-days) produced 15 cancers in comparison to the 1 cancer from the lifetime exposure to 30 ppm (8,700 ppm-days) and no cancers from lifetime exposure to 10 ppm (2,500 ppm-days).

Animals↗
PubMed1980

A Light-dependent Protein Kinase Activity of Chloroplasts.

A protein kinase activity from spinach chloroplasts, tightly associated with the thylakoid membranes, has been solubilized and partially characterized. This membrane-bound protein kinase is stimulated by light and electron transport activity through photosystem II appears to be required for stimulation.Electron transport inhibitors like 3,4-dichlorophenyl-1,1-dimethylurea, Tris, and NH(2)OH treatments, inhibit the light activation process. Furthermore, after Tris inhibition, the protein kinase activity is restored by washing the Tris-treated chloroplasts with dichlorophenol indophenol plus ascorbate. The protein kinase remains active in the dark after short illumination periods, suggesting that a product of electron transport may be involved in light activation.Two endogenous substrates of the protein kinase in thylakoid membranes are the N,N'-dicyclohexylcarbodiimide-reactive proteolipid and the light-harvesting chlorophyll-protein complex. The membrane-bound protein kinase also phosphorylates externally added histone.

Journal Article↗
PubMed1980

Reconstitution of photosynthetic energy conservation. II. Photophosphorylation in liposomes containing photosystem-I reaction center and chloroplast coupling-factor complex.

Photophosphorylation has been reconstituted in a liposomal system containing reaction centers of photosystem I and coupling-factor complex, both highly purified from spinach chloroplasts. This energy-converting model system was put together by diluting the preparation of the coupling-factor complex with an aqueous suspension of proteolipid vesicles, preformed from photosystem-I reaction centers and soybean phospholipids by sonication. In the presence of reduced N-methyl-phenazonium methosulfate the system catalyzed photophosphorylation with rates up to 50 mumol ATP formed x mg chlorophyll-1 x h-1, which was sensitive to uncouplers and to N,N'-dicyclohexyl-carbodiimide. The properties of the system in comparison to chloroplasts is discussed.

Ammonium Chloride↗
PubMed1979

Energy-dependent processing of cytoplasmically made precursors to mitochondrial proteins.

Earlier work has shown that mitochondrial proteins synthesized in the cytosol are initially made as larger precursors which are then transferred into the organelles and processed to their mature size in the absence of protein synthesis. It is now demonstrated that depletion of the mitochondrial matrix ATP in intact yeast spheroplasts by various combinations of inhibitors and mutations prevents the processing of precursors to the three largest subunits of the mitochondrial F1-ATPase and two subunits of the cytochrome bc1 complex. These polypeptides are all synthesized outside the mitochondria and transported to the mitochondrial matrix or inserted into the mitochondrial inner membrane. In contrast, depletion of the matrix ATP does not inhibit processing of the precursor to cytochrome c peroxidase; this enzyme is located in the mitochondrial intermembrane space which is freely accessible to ATP made in the cytosol. The processing of extramitochondrially made precursors or the transfer of these precursors across the mitochondrial inner membrane is thus dependent on ATP.

Adenosine Triphosphate↗
PubMed1978

Prevalence of respiratory abnormalities in a rural and an urban community.

Population samples stratified on sex, age and smoking habits were studied in a rural and an urban community with a low level of air pollution to establish "normal" values of parameters derived from the single-breath N2 curve, the effect of smoking on these parameters, and any differences related to an urban or rural environment. Respiratory symptoms and past illnesses, smoking habits, and residential as well as occupational history were obtained by a respiratory questionnair. Pulmonary function was assessed by the single-breath N2 test and the forced vital capacity maneuver. In "healthy" nonsmokers, residual volume/total lung capacity, closing volume/vital capacity on expiration, and closing capacity/total lung capacity were significantly related to age. The slope of phase III was related to neither height nor age. There was no significant difference in prediction equations between the 2 communities for any of these parameters. Multiple regression analysis indicated that smoking had an effect on residual volume/total lung capacity, closing volume/vital capacity on expiration, closing capacity/total lung capacity, and the slope of phase III in both sexes. Abnormal values were more prevalent among male than female smokers in both communities, the highest prevalence being found in the slope of phase III in both sexes (35 to 40 per cent). The slope of phase III and closing capacity/total lung capacity were consistently related to the current number of cigarettes smoked per day.

Adult↗
PubMed1978

Comments on extrapolation of cancer response from high dose to low dose.

In making judgments as to the cancer risk from low level exposure to carcinogens it is generally necessary to base these judgments on high dose or high incidence data from laboratory or epidemiological studies. The biological considerations involved in making such extrapolations are discussed, as well as some of the mathematical procedures. The difficulties presented by moving from species to species, or from differently acting carcinogenic agents is considered.

Animals↗
PubMed1977

Isolation of a chloroplast N,N'-dicyclohexylcarbodiimide-binding proteolipid, active in proton translocation.

The N,N'-dicyclohexylcarbodiimide-binding proteolipid from lettuce chloroplast membranes has been purified by a novel, rapid technique involving I-butanol extraction and ether precipitation. Reconstitution of this proteolipid into liposomes composed of chloroplast lipids and subsequent incorporation of bacteriorhodopsin resulted in the formation of liposomes exhibiting a light-dependent accumulation of protons. This accumulation was significantly enhanced upon addition of N,N'-dicyclohexylcarbodiimide at concentrations similar to those that inhibit chloroplast adenosinetriphosphatase activity. Radioactively labeled N,N'-dicyclohexylcarbodiimide was found to be incorporated essentially into the proteolipid of the reconstituted liposomes. These results suggest that the functional unit responsible for proton channeling in the chloroplast membrane has been isolated and reconstituted in the native state.

Biological Transport, Active↗