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Biomedical subjects

N Nelson

Publications and source records attributed to N Nelson.

At least 271 records · Page 15Linked to original sources
PubMed1976

Salt inactivation as a mechanistic probe of membrane-bound chloroplast coupling factor 1.

Conditions are reported under which ATP protects membrane-bound coupling factor 1 against sodium bromide inactivation. The presence of Mg2+ was found to be obligatory for this protection. ADP and GTP also protected the enzyme against salt inactivation but to a much smaller extent. Other nucleotides tested were ineffective. At low ATP concentrations ADP prevented the effect of ATP and modified the saturation curve for ATP from hyperbolic to sigmoidal. Treatment of chloroplasts with 0.4 M MgCl2 or 2 M LiCl resulted in inactivation of photophosphorylation. In contrast to NaBr-depleted particles the MgCl2 or LiCl-depleted chloroplasts can be reconstituted by purified coupling factor 1. A binding site for Mg2+ and two different sites for ATP upon the coupling factor 1 are suggested to explain the mechanism of their protection against salt inactivation.

Adenosine Diphosphate↗
PubMed1975

Differentiation between mutants of Escherichia coli K defective in oxidative phosphorylation.

Hybrid membrane particles from two mutants of Escherichia coli K12, Bv4 and K11, defective in oxidative phosphorylation, have been prepared, in which ATP-driven membrane energization is restored. A soluble factor of mutant K11 was found to have properties similar to parental crude coupling factor, ATPase (EC 3.6.1.3). Membrane particles of this mutant could not be reconstituted by parental coupling factor. Either parental coupling factor, or the soluble factor of mutant K11 could reconstitute both respiration-driven and ATP-driven energization to membrane particles of mutant Bv14 or to parental particles depleted of ATPase. Mutant Bv4 was found to be devoid of coupoing factor activity, while retaining the ability to hydrolyze ATP. Both mutants possess an ATPase with an altered binding to the membrane. Mutant K11 is impaired in respiration-driven amino acid transport, in contrast to mutant Bv4. The three major subunits of parental Escherichia coli ATPase have been isolated and antibodies have been prepared against these subunits. Antibodies against the largest subunit (alpha component) or against the intact catalytic subunits (alpha + beta components) inhibit both ATP-Pi exchange in the parent organism as well as ATP hydrolytic activity in parent and mutants. Antibodies against the two other subunits (beta or gamma components) also inhibit these two reactions, but were found to be less effective. Mutant N144, which lacks ATPase activity, shows no precipitin lines with anti-alpha, anti-beta, anti-gamma, or anti (alpha + beta) preparations. In contrast, mutants Bv4 and K11, exhibit cross-reactivity with all of the antisera.

Acridines↗
PubMed1975

Purification and properties of the photosystem I reaction center from chloroplasts.

1. A reaction center from chloroplasts was purified by means of detergent treatment, differential centrifugation, column chromatography, and sucrose gradient. 2. The reaction center is active in NADP photoreduction by ascorbate. Ferredoxin, ferredoxin-NADP-reductase, and plastocyanin were required for the reaction. 3. The preparation contains five classes of polypeptide chains with apparent molecular weights of 70,000, 25,000, 20,000, 18,000 and 16,000 as determined by gel electrophoresis in sodium dodecyl sulfate. 4. Treatment with 0.5% sodium dodecyl sulfate abolished the NADP photoreduction activity and released the low molecular weight subunits, which were removed by sucrose gradient centrifugation from the high molecular weight ones. The P700 signal is associated with the 70,000 molecular weight polypeptide. 5. Antibody, prepared against the active reaction center, inhibited NADP photoreduction catalyzed by the purified reaction center as well as by isolated chloroplasts. The antibody interacted on immunodiffusion plates with any subchloroplast preparation capable of NADP photoreduction. It also interacted with the purified 70,000 molecular weight polypeptide. 6. It is concluded that both the primary oxidation and the primary reduction in Photosystem I are associated with the 70,000 molecular weight polypeptide.

Animals↗
PubMed1975

Laser Raman spectroscopy as a mechanistic probe of the phosphate transfer from adenosine triphosphate in a model system.

Laser Raman spectroscopy has been used to study a phosphate transfer reaction from ATP to Pi or arsenate in dimethyl sulfoxide. The spectra support a mechanism involving Mg-2+ binding to the alpha or beta phosphates of ATP leaving the third phosphate free for the transfer reaction. The data also indicate the formation of a relatively stable intermediate which is facilitated by the presence of dimethyl sulfoxide and a dicarboxylic acid (maleate). The intermediate has a Raman spectrum with a band at 1090.5 cm- minus 1 similar to the end product ADP, but is formed much more rapidly. Since the model reaction has many features in common (e.g., activation by maleate) with the transfer reactions catalyzed by coupling factors from spinach chloroplast, Raman spectroscopy may also prove to be a useful tool in the elucidation of biological energy transfer reactions.

Adenosine Diphosphate↗
PubMed1975

Partial resolution of the enzymes catalyzing photophosphorylation. XV. Approaches to the active site of coupling factor I.

1. Prolonged treatment of coupling factor I (CF1) from spinach chloroplasts with trypsin free of chymotrypsin yielded an active ATPase. The isolated preparation showed only two polypeptide chains (mol wt 55,000 to 60,000) on acrylamide gels run in the presence of sodium dodecyl sulfate. The three smaller subunits of CF1 were not detectable. The preparation no longer served as a coupling factor for photophosphorylation in either EDTA- or silicotungstate-treated chloroplasts. 2. An antiserum prepared against coupling factor I from chloroplasts inhibited the ATPase activity of the trypsin-treated CF1. In contrast, antisera prepared against the two individual (denatured) subunits did not inhibit the ATPase activity when tested either alone or together, although each interacted with the trypsin-treated protein, forming precipitin lines in Ouchterlony plates. 3. The trypsin-treated enzyme was still cold-labile, showing that the three smaller subunits are not required for this property. However, the enzyme was no longer sensitive to the natural inhibitor protein which is one of its subunits (subunit epislon), but was still sensitive to inhibition by the flavonoid quercetin. 4. Two equivalents of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole were sufficient to inhibit about 80% of the ATPase activity of the coupling factor, irrespective of whether it contained two of five subunits. The inhibition was completely reversed by dithiothreitol. 5. Triated 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole was prepared. Treatment of the coupling factor with this tritium-labeled inhibitor followed by electrophoresis on acrylamide gels revealed that most of the radioactivity was incorporated into the beta subunit of the enzyme (molecular weight 56,000).

Adenosine Triphosphatases↗
PubMed1975

Inhalation carcinogenicity of alpha halo ethers. I. The acute inhalation toxicity of chloromethyl methyl ether and bis(chloromethyl)ether.

A range of acute studies were performed with chloromethyl methyl either (CMME) and bis(chloromethyl)ether (BCME), including 14-day LC50's following single seven-hour inhalation exposures. The LC50's for CMME were 55 ppm for rats and 65 ppm for hamsters. The LC50's for BCME were 7 ppm for both species. All animals showed characteristic changes of acute irritation of the respiratory tract manifested by congestion, edema, and hemorrhage. Severe shortening of life span was seen in 30-day exposures of rats to CMME and in all studies with BCME. Incidences of mucosal changes, including atypia, were generally increased in a dose-related manner in both species. The carcinogenicity of BCME in these range finding experiments was demonstrated by a skin cancer in a rat after three exposures and a nasal tumor in a hamster after one exposure to 1 ppm BCME.

Animals↗
PubMed1975

Inhalation carcinogenicity of alpha halo ethers. II. Chronic inhalation studies with chloromethyl methyl ether.

Rats and hamsters were exposed to 1 ppm of chloromethyl methyl ether six hours per day, five days per week, throughout their lifetime. Mortality and weight gain of the exposed animals paralleled that of the control animals. Malignant tumors of the respiratory tract were found in two rats. These were a squamous cell carcinoma of the lung with blood vessel invasion and an esthesloneuroepithelioma originating in the olfactory epithelium and invading the forebrain. One hamster was found to have an adenocarcinoma of the lung and another, a squamous papilloma of the trachea. A single exposed rat had a pituitary tumor of primitive cell type that may well have been coincidental.

Adenocarcinoma↗
PubMed1975

Inhalation carcinogenicity of alpha halo ethers. III. Lifetime and limited period inhalation studies with bis(chloromethyl)ether at 0.1 ppm.

Rats and hamsters were exposed to 0.1 ppm bis(chloromethyl)ether (BCME) six hours per day, five days per week throughout their lifetime. Additional groups of rats were given 10, 20, 40, 60, 80, and 100 exposures to 0.1 ppm BCME and then held until death. Forty cancers originating in the respiratory tract were found in the 200 rats involved in these studies. These included 14 cancers of the lung and 26 cancers of the nasal cavity. They occurred in dose-related fashion. A single undifferentiated carcinoma of the lung was seen in a hamster.

Animals↗
PubMed1975

A combined procedure for preparation of plastocyanin, ferredoxin and CF1.

Homogeneous preparations of ferredoxin, plastocyanin, and chloroplast coupling factor (CF1) have been isolated from spinach by a combined procedure in which supernatants from preparation of chloroplasts are used for isolation of ferredoxin and the chloroplasts serve as the source of plastocyanin. The proteins were purified by DEAE-cellulose chromatography and gel filtration, after precipitation with acetone in the case of ferredoxin or release from membranes in the case of plastocyanin. The proteins obtained by this procedure are pure, as evidenced by absorption ratios (ferredoxin, A420/A276 = 0.47-0.48; plastocyanin, A278/A597 = 1.2) and by the fact that both proteins migrate as single bands on polyacrylamide gels in the presence of sodium dodecyl sulfate.

Chloroplasts↗
PubMed1975

Preparation and properties of chloroplasts depleted of chloroplast coupling factor 1 by sodium bromide treatment.

Chloroplasts were treated with 2 m sodium bromide. The resulting particles lost their ATPase activity and chloroplast coupling factor 1 subunits were detected in the supernatant by means of gel electrophoresis and specific antibodies. The chloroplast coupling factor 1 depleted particles show high rates of Hill reaction with pH optimum shifted toward lower pH. The sodium bromide treatment also abolished the light-induced proton uptake. In the presence of N-methylphenazonium methosulfate light-induced proton release, insensitive to uncouplers, was observed. Addition of dicyclohexylcarbodiimide reversed the light-induced pH changes to the normal proton uptake and increased the pH optimum of the Hill reaction.

Journal Article↗
PubMed1975

Mortality patterns among workers exposed to chloromethyl ethers--a preliminary report.

Chloromethyl methyl ether (CMME) has been used extensively as a crosslinking agent for ion-exchange resins. Commercial grades of CMME are contaminated to the extent of 2-8% with bischloromethyl ether, an alkylating agent which has been shown to be a very potent lung carcinogen in animals. Reports by other investigators in this and other countries have implicated CMME as a lung carcinogen in chemical workers. The purpose of the study reported here was to examine the lung cancer mortality experience with respect to intensity and duration of exposure in six of the seven chemical companies that account for virtually all of the CMME use in the United States. The study included about 1800 workers who were exposed in the period 1948 to 1972 and about 8000 workers not exposed to CMME from the same plants who served as controls. Exposed workers were characterized according to job description and duration of exposure. In several plants the intensity of exposure was numerically graded for each job category with adjustment for temporal changes in the plant processes. Social Security records were used to identify deaths among workers who had left the companies and death certificates have been obtained for virtually all known deaths. The age-adjusted death rate for respiratory cancer in the CMME exposed group as a whole was 2.5 times that in the control group, whereas death rates due to other causes were comparable. There was also a gradation of lung cancer risk according to intensity and duration of exposure and the time elapsed since the onset of exposure.

Adolescent↗
PubMed1975

Health effects of fossil fuel combustion products: report of a workshop.

Judgemental positions are presented on research priorities in regard to the health effects from stationary sources of fossil fuel combustion products. Hopefully, they can provide guidance for efforts to ensure that national energy needs are met with minimum environmental and economic burdens on the public. The major areas include epidemiological studies, controlled biological studies, mutagenesis and carcinogenesis, trace elements, monitoring and analysis.

Animals↗
PubMed1974

Purification and properties of Mg2+-Ca2+ adenosinetriphosphatase from Escherichia coli.

A procedure for the purification of Mg(2+)-Ca(2+) adenosinetriphosphatase (EC 3.6.1.3) from E. coli, yielding relatively large amounts of highly active enzyme, is described. The enzyme consists of four nonidentical subunits. Trypsin treatment of purified enzyme yields a preparation consisting exclusively of the two larger subunits, which are sufficient for ATPase activity. Purified enzyme is inhibited by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole; this inhibition is reversed by dithiothreitol, and the diazole is found preferentially associated with the beta-subunit of the enzyme. Antibody prepared against the trypsin-treated enzyme inhibited various ATP-dependent reactions as well as membrane-bound ATPase itself.

Adenosine Diphosphate↗