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Biomedical subjects

J L Ramos

Publications and source records attributed to J L Ramos.

At least 145 records · Page 8Linked to original sources
PubMed1985

Lesions in citrate synthase that affect aerobic nitrogen fixation by Azotobacter chroococcum.

A class of Azotobacter chroococcum mutants induced by Tn1 that were defective in normal aerobic nitrogen fixation when grown on sugars (Fos-) were corrected by provision of alpha-ketoglutarate or glutamate. In a representative mutant, Fos252, rates of evolution of 14CO2 from [14C]acetate or [14C]glucose were 5% of the parental values, although uptake and incorporation were normal for both substrates. The results suggest that a lesion affects the entry of substrates into the tricarboxylic acid cycle. The activity of citrate synthase in Fos252 in vitro was 5% that of the parents. The citrate synthase (gltA) gene from Escherichia coli was cloned into broad-host-range vectors and mobilized into Fos252. The plasmids restored parental citrate synthase activities to Fos252 and complemented the inability to fix N2 in air. The data indicate that a mutation causing an intrinsic limitation in respiratory capacity abolishes normal aerobic N2 fixation, which is consistent with the hypothesis of respiratory protection for nitrogenase in Azotobacter species.

Azotobacter↗
PubMed1984

Sustained Photoproduction of Ammonia from Dinitrogen and Water by the Nitrogen-Fixing Cyanobacterium Anabaena sp. Strain ATCC 33047.

Conditions have been developed that lengthen the time during which photosynthetic dinitrogen fixation by filaments of the cyanobacterium Anabaena sp. strain ATCC 33047 proceeds freely, whereas the subsequent conversion of ammonia into organic nitrogen remains blocked, with the resulting ammonia released to the outer medium. When l-methionine-dl-sulfoximine was added every 20 h, maximal rates of ammonia production (25 to 30 mumol/mg of chlorophyll per h) were maintained for about 50 h. After this time, ammonia production ceased due to a deficiency of glutamine and other nitrogenous compounds in the filaments, conditions which finally led to cell lysis. The effective ammonia production period could be further extended to about 7 days by adding a small amount of glutamine at the end of a 40-h production period or by allowing the cells to recover for 8 h in the absence of l-methionine-dl-sulfoximine after every 40-h period in the presence of the inhibitor. A more prolonged steady production of ammonia, lasting for longer than 2 weeks, was achieved by alternating treatments with the glutamine synthetase inhibitors l-methionine-dl-sulfoximine and phosphinothricin, provided that 8-h recovery periods in the absence of either compound were also alternated throughout. The biochemically manipulated cyanobacterial filaments thus represent a system that is relatively stable with time for the conversion of light energy into chemical energy, with the net generation of a valuable fuel and fertilizer through the photoreduction of dinitrogen to ammonia.

Journal Article↗
PubMed1982

Optimization of Conditions for Photoproduction of Ammonia from Nitrate by Anacystis nidulans.

The effect of several relevant environmental factors influencing the photoproduction of ammonia from nitrate by Anacystis nidulans cells treated with the glutamine synthetase inhibitor l-methionine-dl-sulfoximine has been investigated. The optimal ratio between l-methionine-dl-sulfoximine concentration (micro-molar) and cell density (micrograms of chlorophyll per milliliter) was around 1, the process taking place at maximal rate at a temperature of about 40 degrees C, within the pH range of 7 to 10. Ammonia production was stimulated by CO(2) or bicarbonate and was not affected by the accumulation of ammonia in the medium up to concentrations of 30 mM. The rate of ammonia production was found to be determined by the interaction of at least four factors, namely, irradiance and the density, depth, and turbulence of the cell suspension. Ammonia photoproduction from nitrate and water represents an interesting process for the conversion of light energy into chemical energy, which can operate at high efficiency, around 30% of its theoretical maximum.

Journal Article↗
PubMed1982

Sustained Photoproduction of Ammonia from Nitrate by Anacystis nidulans.

Conditions that lengthen the time during which l-methionine-dl-sulfoximine (MSX) promotes excretion of ammonia produced by photosynthetic nitrate reduction in Anacystis nidulans have been sought. If MSX was added every 24 h, maximal rates of ammonia production were maintained for 3 days. After this time, ammonia production ceased due to a specific deficiency of glutamine in the cells, which finally led to cell lysis. The effective ammonia production period could be further extended either by adding a low amount of glutamine at the end of the 3-day period or by allowing the cells to recover for 8 h in the absence of MSX after every 48-h period in the presence of inhibitor. In this way, a steady production of ammonia lasting for at least 10 days was achieved. The MSX-treated cyanobacterial cells thus represent a system relatively stable with time for the conversion of light energy into chemical energy through the photoreduction of nitrate to ammonia.

Journal Article↗
PubMed1979

[Progressive antithrombin activity in blood of pregnant women and neonates in the first four days of life (author's transl)].

Progressive antighrombin activity was assayed in 45 term infants in the first four days of life, in 20 cord blood specimens and in the blood of 20 pregnant women (at term). In the term infants a positive correlation was shown between progressive antithrombin and postnatal age. No correlation could be demonstrated with sex, ethnic group or type of delivery. Maternal antithrombin activity was shown to be moderately decreased, maternal values being closely related to cord blood values.

Antithrombin III↗