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Biomedical subjects

N G Carr

Publications and source records attributed to N G Carr.

At least 37 records · Page 2Linked to original sources
PubMed1978

Changes in photosynthetic activity in the cyanobacterium Chlorogloea fritschii following transition from dark to light growth.

The cyanobacterium Chlorogloea fritschii loses Photosystem II activity, measured by delayed fluorescence and oxygen evolution, during dark heterotrophic growth, but retains Photosystem I, measured as light induced EPR signals. Following transition to the light, Photosystem II recovers in two stages, the first of which does not require protein synthesis. New Photosystem I reaction centres are not synthesised until after net chlorophyll synthesis has commenced. Carbon dioxide fixation recovery commences immediately, the initial rate being unaffected by chloramphenicol. The recovery of carbon dioxide fixation is not directly related to oxygen evolution rate and is only inhibited slightly by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone.

Chloramphenicol↗
PubMed1977

Identification of a non-magnetic iron centre and an iron-storage or -transport material in blue--green algal membranes by Mössbauer spectroscopy.

At least two species of iron were identified in crude membrane preparations of the blue-green algae Chlorogloea fritschii and Anacystis nidulans by Mössbauer spectroscopy. One species was non-magnetic with chemical shift more characteristic of a ferredoxin-like centre than of any known low-spin Fe(II) biological compounds. Studies on cells grown under depleted-iron conditions show the other iron species to be part of the system for iron metabolic transport and/or storage.

Cell Membrane↗
PubMed1977

The regulation of stable RNA synthesis in the blue-green alga Anacystis nidulans: effect of leucine deprivation and 5-methyltryptophan inhibition.

The expression of phenomena associated with the bacterial function controlling RNA synthesis was studied in leucine-deprived or 5-methyltryptophan-treated cultures of Anacystis nidulans. Both procedures retarded cell growth, RNA and protein accumulation, elicited the accumulation of high intracellular concentrations of guanosine 5'-diphosphate-3'-diphosphate(ppGpp)and guanosine5'-triphosphate-3'-diphosphate(pppGpp),and promoted a regime of non-coordinate synthesis of stable and messenger RNA. The rate of polymerization of nascent RNA chains did not appear to be retarded in the growth-limited cultures.

Cyanobacteria↗
PubMed1976

Heterocyst and nitrogenase development in Anabaena cylindrica.

The differentiation of filaments of a continuous culture of Anabaena cylindrica after removal of fixed nitrogen has been examined. Rapid development of proheterocysts (4-5 h) and mature heterocysts (14 h) in an ordered sequence was observed; the development of the latter was concomitant with the onset of nitrogenase activity. Commitment times of 2-3 h (proheterocyst) and 5-0 (heterocyst) were measured. Evidence is presented that shows that heterocyst development, rather than any product of heterocyst function in nitrogen fixation, is responsible for the imposition of the pattern of heterocysts in a filament of vegative cells. Both phycocyanin content and carbon dioxide fixation declined markedly throughout the filament during the early stages of heterocyst development, indicating that all the cells of the filament are involved in the initial stages of the differentiation process. Heterocysts do not evolve oxygen in the light, but do respire. Nitrogenase activity in isolated heterocysts and in intact filaments was stimulated by phosphoenolpyruvate, ATP and dichlorophenolindophenol-ascorbate.

2,6-Dichloroindophenol↗
PubMed1975

RNA synthesis and the accumulation of guanine nucleotides during growth shift down in the blue-green alga Anacystis nidulans.

Shift down of growth rate in the blue-green alga Anacystis nidulans by reduction of the incident light intensity produced a reduction in the rate of stable RNA accumulation which was correlated with increased concentrations of three phosphorylated compounds, two of which were identified as guanosine 5'-diphosphate-3'-diphosphate (ppGpp) and guanosine 5'-triphosphate3'-diphosphate (pppGpp). The step also causes a large but transient increase in the concentration of GTP. Stable RNA fails to accumulate for a considerable length of time after the concentrations of ppGpp and pppGpp have fallen, suggesting the involvement of another mechanism in the control of stable RNA accumulation.

Cyanobacteria↗
PubMed1975

Temporal genetic mapping in the blue-green alga Anacystis nidulans using ethyl methanesulphonate.

Cultures of the blue-green alga Anacytis nidulans were synchronized with respect to DNA synthesis as well as cell division. Application of ethyl methanesulphonate at different stages of replication resulted in a peak of mutation frequency for different genetic markers; this peak can be accounted for in terms of the involvement of repair processes. A temporal map of 19 markers has been constructed by this method. Comparison of gene position obtained by temporal mapping indicates that either bidirectional replication or unidirectional replication from more than one origin occurs.

Cell Division↗
PubMed1974

A new method for the preparation of uniformly 14C-labelled compounds by using Anacystis nidulans.

1. Growth conditions were devised which enabled Anacystis nidulans to be grown on high specific radioactivity (14)CO(2) (at over 98% isotopic abundance of (14)C) in a closed system with greater than 85% substrate utilization. 2. The DNA and RNA content of A. nidulans was estimated by various methods and compared with that of Chlorella pyrenoidosa. 3. A procedure was developed for the quantitative extraction and separation of the DNA and RNA from A. nidulans. 4. The fractionation and analysis of the DNA and RNA includes methods for the preparation of the uniformly (14)C-labelled deoxyribonucleoside monophosphates and the uniformly (14)C-labelled ribonucleoside monophosphates. 5. The base 6-methylaminopurine was identified as a component of the DNA. 6. The preparation and total yield of uniformly (14)C-labelled amino acids from A. nidulans are also briefly described. The results are discussed in relation to the use of other micro-organisms for the preparation of compounds labelled with (14)C.

Adenosine Monophosphate↗