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Biomedical subjects

N Nelson

Publications and source records attributed to N Nelson.

At least 235 records · Page 13Linked to original sources
PubMed1983

Photosystem I reaction center from the thermophilic cyanobacterium Mastigocladus laminosus.

Photosystem I reaction center was isolated from the cyanobacterium Mastigocladus laminosus. It contained four different subunits with molecular masses (as determined by sodium dodecyl sulfate gels) of about 70,000 (subunit I), 16,000 (subunit II), 11,000 (subunit III), and 10,000 (subunit IV) daltons. The purified reaction center contained about 100 chlorophyll a molecules per P(700); however, they could be readily depleted down to about 50 chlorophyll a per P(700) without loss in the photochemical activities. The reaction center was active in cytochrome c photooxidation, but the photooxidation of an acidic cytochrome, like the Euglena cytochrome 552, required the presence of cations. The purified reaction center was found to be similar in several respects to the photosystem I reaction centers from higher plants and, especially, to the one isolated from green algae. Subunit I appeared on sodium dodecyl sulfate gels in the same position and possessed the same shape of an apparent double band as the corresponding subunits I of green plants and of algae. Subunits I and II of photosystem I reaction centers from Mastigocladus, higher plants, and green algae showed immunological crossreactivity. This observation might serve as biochemical evidence for the common evolution of the photosystem I reaction centers. In higher plants and green algae subunit II is a product of cytoplasmic ribosomes and therefore, a high degree of homology should have been preserved upon transfer of its gene from the prokaryote to the nucleus of the eukaryotes.

Journal Article↗
PubMed1983

Differential Changes in the Amount of Protein Complexes in the Chloroplast Membrane during Senescence of Oat and Bean Leaves.

Antibodies against the individual subunits of protein complexes in the chloroplast membranes were used to follow the amounts of these polypeptides during foliar senescence. No change was found in the amount of polypeptides of photosystem I reaction center and the chloroplast coupling factor during senescence of oat (Avena sativa L.) and bean (Phaseolus vulgaris L.) leaves. A significant decrease in the amount of the different components of the cytochrome b(6)-f complex was detected. This change may account for the decrease in the rate of electron transport, which might be the rate limiting step of photosynthesis in senescing leaves.

Journal Article↗
PubMed1982

Proteolipid of adenosinetriphosphatase from yeast mitochondria forms proton-selective channels in planar lipid bilayers.

Proteolipid isolated from yeast mitochondrial adenosinetriphosphatase by butanol extraction is reincorporated into lipid vesicles from which planar membranes are formed. The proteolipid permits electric conductance through the membrane. This conductance occurs through membrane channels which are highly selective for protons. Proton channels in the membrane are directly observed at high proton concentrations in the aqueous phases. Channels open and close independently from each other; their open-state conductances and lifetimes are monodisperse but influenced by the applied voltage (12 pS and 3 s, respectively, at pH 2.2 and 100 mV). Proton channels do not occur in single proteolipid molecules; the conducting structure consists of at least two polypeptide chains since channels form in a (reversible) bimolecular reaction of nonconducting forms of proteolipid. The number of proton channels at a constant proteolipid concentration changes in sharp transitions and by orders of magnitudes upon critical changes of membrane composition and pH. These transitions are caused by transitions of proteolipid organization in the membrane from a dispersed state (equilibrium between channel-forming "dimers" and a large pool of "monomers") to a state of almost complete aggregation of proteolipid which stabilizes large proton-conducting structures (probably associates of channel-forming dimers). This self-association of isolated proteolipid into structures containing proton-selective channels suggests that the six proteolipids in the adenosinetriphosphatase complex exist as a self-associating entity containing most likely three proton channels.

Adenosine Triphosphatases↗
PubMed1982

Hyperbilirubinemia in Inuit neonates.

A prospective study was undertaken to determine if Inuit and Caucasian neonates have different patterns of physiologic jaundice. Daily blood samples obtained by heel pricks of Inuit and Caucasian neonates born at the Churchill (Man.) Health Centre were assayed for the total serum bilirubin concentration. The mean peak bilirubin level in the Inuit group was significantly higher than that in the Caucasian group (8.76 v. 6.04 mg/dl [150 v. 103 mumol/l]) and occurred later (on day 3 rather than day 2). Of the Caucasian neonates, those who were breast-fed in hospital had a significantly higher (P less than 0.05) mean peak bilirubin level than those who were not, and among all the neonates who were not breast-fed in hospital the Inuit had a significantly higher mean peak bilirubin level than the Caucasians (7.98 v. 3.64 mg/dl [136 v. 62 mumol/l]). These findings indicate that factors other than breastfeeding, some of which may be genetic, are responsible for the higher and later peak in the serum bilirubin concentration in Inuit neonates.

Bilirubin↗
PubMed1982

Properties of a novel ATPase enzyme in chromaffin granules.

Membranes were isolated from mitochondria and chromaffin granules of bovine adrenal medullae. The cross-contamination between the two membranes was examined by comparing the radioactive bands on autoradiograms of gels after phosphorylation of the membranes with [gamma-32P]-ATP and decoration with [125I]concanavalin A and [125I]protein A with antibody that was raised against chromaffin-granule membranes. It was found that the membranes cross-contaminated each other by less than 10%. The technique of immunodecoration with antibodies against beta subunits of proton-ATPases from yeast mitochondria, spinach chloroplasts, and E. coli membranes was used for quantitative estimation of proton-ATPase complexes in chromaffin granules and mitochondrial membranes. It was found that chromaffin-granule membranes contain less than 10% of the amount of proton-ATPase complex in mitochondrial membranes. The specific ATPase activity of chromaffin-granule membranes was on the order of 30 to 50% of the mitochondrial membranes. The ATPase activity of the chromaffin-granule membranes was more sensitive to 4-acetamido-4'-isothiocyano-2,2'-disulfonic acid stilbene and 4-chloro-7-nitrobenzofurazan. It was much less sensitive than the mitochondrial membranes to antibody against beta subunit of proton-ATPase from E. coli membranes. After solubilization of chromaffin-granule membranes by octyglucoside and cholate and subsequent centrifugation on sucrose gradient, two different ATPase enzymes were separated. The heavier enzyme was identical to the mitochondrial-ATPase complex, while the lighter enzyme was identified as a novel ATPase, which might be responsible for the special properties of the ATPase activity of chromaffin-granule membranes.

Adenosine Triphosphatases↗
PubMed1982

Myelogenous leukemia in rodents inhaling benzene.

Studies during the past five decades have failed to demonstrate myelogenous leukemia in laboratory animals exposed to benzene despite epidemiologic evidence linking such exposure to myelogenous leukemia in man. We report four cases of myeloproliferative disease among rodents exposed to benzene, 6 h a day, 5 days weekly, for life. There was one case of chronic myelogenous leukemia, one of acute myeloblastic leukemia, and one of granulocytic hyperplasia among 40 CD-1 mice exposed to 300 ppm benzene; and one case of chronic myelogenous leukemia among 40 rats exposed to 100 ppm benzene. Although not statistically significant as compared to the respective control groups, the fact that myelogenous leukemia has not been reported in control animals of these two strains is suggestive of a causative role for benzene.

Animals↗
PubMed1982

Catheter colonization and bacteremia with pulmonary and arterial catheters.

We prospectively studied the incidence of catheter-related sepsis in 51 critically ill patients who underwent 52 arterial and 37 pulmonary artery catheterizations over a period of 3 months. Daily cultures of blood and catheter insertion site were done and the catheters were cultured semiquantitatively at the time of removal. Catheter colonization defined as growth of 15 or more colonies was observed with 9 (10%) catheters and bacteremia with 4 (4.5%) catheters. The skin cultures were positive in 56% of the colonized catheters compared with 11% of sterile catheters (p less than 0.01). The mean duration of catheterization of 3.8 days in colonized catheters was not different than 3.3 days in noncolonized catheters. Presence of concurrent infection and use of antibiotic did not change the rate of catheter colonization. Often, microorganisms other than those colonizing the catheter were recovered from blood. Femoral arterial catheterization appeared to be more often associated with colonization than radial catheters. It appears that the arterial and pulmonary artery catheter colonization occurs in about 10% of catheters and predisposes to catheter-related sepsis. Semiquantitative cultures of the catheter may aid in better documentation of catheter-induced sepsis.

Arteries↗
PubMed1982

Gaseous formaldehyde and hydrogen chloride induction of nasal cancer in the rat.

The carcinogenic response to the combined and separate exposures to formaldehyde (HCHO) and hydrochloric acid (HCl) was investigated in male inbred SD rats. The rats were exposed to gaseous HCHO, 14 ppm, and HCl, 10 ppm, in two experiments. In one experiment the gases were premixed at high concentrations before being diluted in the exposure chamber air to maximize the formation of the carcinogen bis(chloromethyl)ether (BCME). In the second experiment exposure was repeated to HCl and HCHO premixed at high concentrations, and not premixed (to minimize BCME formation), as well as to HCHO alone and HCl alone. The second experiment is being reported on at an interim stage. HCHO alone induced squamous carcinomas of the nasal cavity as did the combined exposures to HCHO and HCl. No carcinogenic response was observed with HCl alone. HCHO accounted for most, if not all, of the carcinogenic activity of the mixture of HCHO-HCl.

Animals↗
PubMed1981

Purification properties and biogenesis of Chlamydomonas reinhardii photosystem I reaction center.

A photosystem I reaction center was isolated from Chlamydomonas reinhardii chloroplasts. It consists of four different polypeptides with Mr approximately 70,000 (subunit I), 19,000 (subunit II), 10,000 (subunit III), and 8,000 (subunit IV). In the presence of salts, the purified reaction center was active in cytochrome 552 photooxidation. Short term labeling experiments with [35S]sulfate revealed that subunit III contains no cysteine or methionine. Subunits I and IV were shown to be chloroplast translation products, while subunit II appears to be synthesized on cytoplasmic ribosomes. The site of synthesis of the subunits to the proton-ATPase complex was studied. A differential effect of cycloheximide on the assembly of photosystem I reaction center and the proton-ATPase complex was indicated.

Chlamydomonas↗
PubMed1981

Purification and immunological properties of proton-ATPase complexes from yeast and rat liver mitochondria.

Proton-ATPase complexes from yeast and rat liver mitochondria were isolated by a simple method previously employed for the purification of the proton-ATPase complex from chloroplasts. After reconstitution into liposomes, the purified complexes were active in the ATP-Pi exchange reaction, the rate of which was 120 and at least 200 nmol/mg of protein/min for the rat liver and yeast mitochondria ATPases, respectively. Upon sodium dodecyl sulfate polyacrylamide gel electrophoresis, each complex exhibited 11 to 12 different polypeptides. The isolated ATPase complexes from rat liver and yeast mitochondria, from Swiss chard chloroplasts, and Escherichia coli membranes were reacted with antibodies prepared against the various subunits of ATPase complexes. From all the combinations of antigen-antibody examined, only the antibodies against beta subunit cross-reacted with the corresponding subunit of all the ATPase complexes tested. These results indicate that certain amino acid sequences in the beta subunit have been preserved in all of the proton-ATPase complexes.

Adenosine Triphosphatases↗
PubMed1981

Cancer prevention: environmental, industrial, and occupational factors.

The possible contribution of occupational and environmental exposures to cancer has been known for many years and is now a highly mature field of study. By the 1950s, a substantial list of agents of processes had been identified as associated with cancer of one organ or another. In the last several decades a number of additions have been made to the list. No doubt more will be found in the future. The last decade, especially, has brought increased public attention to cancer in the workplace. The Occupational Safety and Health Act of 1970 has been a significant contributor to the current increase in attention given to cancer occurrences arising from occupational exposures. These have led to increasingly stringent regulations and control requirements. The nature of the chemical and physical factors in occupational cancer will be noted and the estimates of the contribution of occupational factors to total cancer occurrence will be considered. In addition to the workplace exposures, other ways in which cancer may be associated with technology will be described. Included among these are, community air pollution, water contaminants, dietary additives, and hair dyes.

Air Pollutants↗
PubMed1981

Photosystem I reaction centers from Chlamydomonas and higher plant chloroplasts.

A photosystem I reaction center has been isolated from Chlamydomonas chloroplasts and compared with the photosystem I reaction center from higher plants. While the higher plant reaction center is active in cytochrome 552 photooxidation, the Chlamydomonas preparation was not active unless salts were included in the assay medium or the pH was lowered to 5. Subunit III-depleted photosystem I reaction center from higher plants is also inactive in cytochrome 552 photooxidation in the absence of salts. As with the Chlamydomonas reaction center, salts induced its activity. Subunit I of the photosystem I reaction center has tentatively been identified as the binding site of cytochrome 552.

Chlamydomonas↗
PubMed1980

Biosynthesis and assembly of the proton-translocating adenosine triphosphatase complex from chloroplasts.

The H(+)-translocating ATPase complex of chloroplasts consists of at least eight nonidentical subunits. Five of these (alpha, beta, gamma, delta, and epsilon subunits) collectively constitute the globular extramembranous CF(1) portion of the complex. The remaining three subunits (I-III) represent the membrane-embedded portion. Biosynthesis and assembly of these subunits were studied by pulse-labeling isolated spinach chloroplasts in the presence of cycloheximide or chloramphenicol and by translating total leaf RNA in a rabbit reticulocyte system. The labeled products were analyzed by immunoprecipitation with subunit-specific antisera or by isolating the entire H(+)-translocating ATPase complex in a nearly pure state. We found that chloroplasts synthesize the alpha, beta, gamma, and epsilon subunits of CF(1), the membrane-embedded subunit I, and probably also the membrane-embedded subunit III. The delta subunit (and probably also subunit II) are imported from the cytoplasm via larger precursor forms. After isolated chloroplasts are labeled in the presence of cycloheximide, the chloroplast-made H(+)-ATPase subunits are assembled into a complex that is indistinguishable from the authentic H(+)-ATPase complex. This assembly indicates that isolated chloroplasts contain excess pools of the cytoplasmically made subunits.

Journal Article↗
PubMed1980

Reconstitution of purified acetylcholine receptors with functional ion channels in planar lipid bilayers.

Acetylcholine receptor, solubilized and purified from Torpedo californica electric organ under conditions that preserve the activity of its ion channel, was reconstituted into vesicles of soybean lipid by the cholate-dialysis technique. The reconstituted vesicles were then spread into monolayers at an air-water interface and planar bilayers were subsequently formed by apposition of two monolayers. Addition of carbamoylcholine caused an increase in membrane conductance that was transient and relaxed spontaneously to the base level (i.e., became desensitized). The response to carbamoylcholine was dose dependent and competitively inhibited by curare. Fluctuations of membrane conductance corresponding to the opening and closing of receptor channels were observed. Fluctuation analysis indicated a single-channel conductance of 16 +/- 3 pS (in 0.1 M NaCl) with a mean channel open time estimated to be 35 +/- 5 ms. Thus, purified acetylcholine receptor reconstituted into lipid bilayers exhibited the pharmacological specificity, activation, and desensitization properties expected of this receptor in native membranes.

Animals↗