Photosynthesis as a resource for energy and materials.
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Carbohydrates↗
Biomedical subjects
M Calvin
Publications and source records attributed to M Calvin.
Inhibition of infectious Rous sarcoma virus production by rifamycin derivative.
A new rifamycin derivative, rifazone-82 (R-82), an inhibitor of viral RNA-dependent DNA polymerase, is selectively toxic to transformed chicken cells in culture. R-82 has now been shown to possess antiviral activity as well. The relatively nontoxic properties of R-82 to nontransformed cells have permitted the execution of experiments examining the effect of a rifamycin derivative on virus reproduction. Addition of low concentrations of R-82 (15 mug/ml) to cultures soon after Rous sarcoma virus infection prevents the spread of infection thoroughout the culture. This inhibition is not dependent on concomitant cellular transformation as identical results were obtained with cells infected with a transformation-defective Rous sarcoma virus. Addition of R-82 to cultures in which all the cells are infected does not substantially affect the yield of physical particles as measured by RNA-dependent DNA polymerase activity and by (3H) uridine incorporation into viral RNA. However, the infectivity of the progeny virus, as measured by focus-forming ability, is decrreased 95 to 99% by R-82 treatment.
Animals↗
Quantitative studies of the toxicity of benzo(a)pyrene to a mouse liver epithelial cell strain in culture.
The toxic effects of the carcinogen benzo(a)pyrene (BaP) were studied in a well-characterized epithelial cell strain NMuLi, derived from the livers of weanling Namru mice. These cells were extremely susceptible to the toxicity, 99% dying after a 6-day exposure to BaP, 5mug/ml. The toxic effects began between 11 and 24 hr postapplication of BaP to the cells and increased exponentially with the time of treatment. The toxicity was concentration dependent in cells treated for a specific time period. The survival curves were exponential and extrapolated to a survival fraction of 1.0. The toxic effects of BaP to logarithmically growing NMuLi were inhibited 40% by 7,8 benzoflavone, and the inhibition was concentration dependent. The 7,8-benzoflavone also inhibited aryl hydrocarbon hydroxylase (AHH) from NMuLi cell homogenates and microsomes by 99%. The concentration dependence for AHH inhibition by 7,8-benzoflavone paralleled its inhibition of cellular toxicity. The toxicity of BaP to these cells increased exponentially with the number of population doublings. Hence, the toxicity was 130 times greater in exponentially growing cells than in confluent cells. Levels of AHH, the enzyme that metabolizes BaP to its cytotoxic derivatives, were only 2.4 times higher in exponentially growing than in confluent cells, suggesting that cell division was responsible for the large differential toxicity. In addition, a toxic BaP metabolite was preferentially toxic to log-phase cells. The results indicate that the metabolism of BaP by AHH to produce cytotoxic metabolites, which may cause lesions that are expressed upon cell division, is responsible for the cytotoxicity of BaP to NMuLi.
Animals↗
Tritium incorporation at specific positions in benzo(a)pyrene.
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Benzopyrenes↗
Carcinogenesis.
An examination has been made of the major chemicals which are known to be carcinogenic, either in animals or in humans. As a result, a generalized type of chemical property seems to be a prerequisite for the carcinogenic activity. In most cases, this is some kind of reactive electrophilic intermediate produced directly from the carcinogen or from one of its immediate metabolites. This electrophilic reagent is generally a positively charged ion of some kind. In the case of the hydrocarbons it seems to be an incipient carbonium ion; in the case of nitrogen compounds, it is a corresponding nitronium ion. There are a number of possible substrate materials (nucleophilic) in a cells, but the dominant one which has been suspected is the nucleic acid component, either the DNA or the RNA. The bases of these materials all have extra pi electrons susceptible to attach by the electrophiles of the carcinogen. Such a modification, particularly of the DNA, could lead to either major or minor changes in the genetic composition of the cell. Minor changes are usually rectifiable or are not visible, and this would include a large variety of point mutations.
2-Acetylaminofluorene↗
Stabilization of electron spin resonance probes for photosynthesis studies.
The major obstacle to the study of functional/structural interrelationships of spinach chloroplasts by using spin labels has been the rapid loss of the electron paramagnetic resonance (EPR) signals upon illumination with visible light. The present study demonstrates that the addition of ferredoxin and NADP+ in the presence of N-tris(hydroxymethyl)methylglycine (Tricine) buffer at pH 7.1 or higher mitigates the rapid loss of Biradical X [N,N'-bis(1-oxyl - 2,2,5,5 - tetramethylpyrroline-3-carboxy)-1,2-diaminoethane] and Monradical A (2,2,5,5-tetramethyl-3-carbamidpyrroline-1-oxyl). However, the 5-line EPR spectrum characteristic of Biradical X in aqueous solution was changed to a dominantly 3-line spectrum within a few minutes after illumination in the presence of ferredoxin and NADP+. Analysis of the double integration of the first derivative EPR spectrum revealed no decrease in Biradical X concentration for more than 30 min of illumination. Our data suggest that Biradical X attaches to some soluble macromolecule(s) and that illumination of chloroplasts promotes such an attachment.
Chloroplasts↗
A simple method for freeze-fracture of monolayer cultures.
A simple method is described for the freeze-fracture in situ of monolayer cultures grown on gold carriers coated with a thin layer of silicon monoxide. Preliminary observations on 3T3 mouse embryo fibroblasts indicate that this technique exposes large areas of cell membrane, making it possible to determine how areas of membrane specialization are related to the cell as a whole and to regions of cellular interaction. 3T3 cells cultured on silicon monoxide show no modification of growth properties compared to cells growing on Falcon plastic, and other cell lines also appear to grow well on this substrate.
Cell Division↗
Benzo(alpha)pyrene effects on mouse epithelial cells in culture.
The effect of benzo (a) pyrene on the growth in culture of 5 mouse epithelial cell strains was examined. These epithelial cells are highly sensitive to the cytotoxic action of benzo (a)-pyrene. In addition, the activity of the benzol (a) pyrene-metabolizing system, aryl hydrocarbon hydroxylase, is low but highly iducible by the carcinogen. As the sensitivity of a cell strain to the cytotoxic action of benjo (a) pyrene decreased, the inudcibility of the hydroxylase also decreased,. However, a strong correlation could not be found between cytotoxicity and the level of uninduced or induced hydroxylase when the values from different cell strains were compared. These experiments suggest that thehydroxylase is important in determining the sensitivity of epithelial cells to the cytotoxic action of benzo (a) pyrene, but other factors may also modulate this sensitivity.
Animals↗
Chemical evolution.
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Biochemical Phenomena↗