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Biomedical subjects

J Myers

Publications and source records attributed to J Myers.

At least 289 records · Page 16Linked to original sources
PubMed1966

Monochromatic light saturation curves for photosynthesis in Chlorella.

We used a small oxygen electrode and a grating monochromator of 10 mmu half-band width to determine light-saturation curves of photosynthesis for films of Chlorella pyrenoidosa no more than 1 cell thick. All curves were referenced to the lightsaturated rate observed in 5 mw/cm(2) of 680 mmu. To a close approximation (+/- 2%) the light-saturated rate was independent of wavelength over the region in which light intensity was sufficient to make the test (450-705 mmu). At wavelengths of high absorption we obtained intensities sufficient to cause photoinhibition. As a measure of photoinhibition we used the breakpoint, the lowest intensity at which rate of photosynthesis decreased with time. In general, the saturated rate was slightly lower and the estimated breakpoint was considerably lower at wavelengths of high absorption. Maximum rate of absorption of quanta at the breakpoint was highest in the far-red (>/= 700 mmu), lower and relatively constant in the near-red (630-680 mmu), and lowest in the blue. At 435 and 450 mmu the breakpoint occurred below saturation. We attribute small deviations in maximum rate of photosynthesis to effects of photoinhibition. Independence of wavelength observed for the light-saturated rate is consistent with models of photosynthesis in which maximum rate is limited by the same dark reaction at all wavelengths.

Eukaryota↗
PubMed1966

Stimulation of photophosphorylation and cytochrome c photooxidation by pteridines.

A number of pteridines were examined for activity in promoting photophosphorylation in broken spinach chloroplasts and in stimulating cytochrome c photooxidation in sonicated chloroplasts. Correlation was found between activities for the 2 reactions. Photophosphorylation promoted by pteridines was inhibited by DCMU and by anaerobic conditions. It is concluded that pteridines may stimulate photophosphorylation by linking photosystem 1 with molecular oxygen and thereby allowing noncyclic electron flow. Aromatic pteridines in both the 2,4-dihidroxy- and 2-amino-4-hydroxy-series were active; substitution at the 6 (or 7) position was a necessary but not sufficient condition for activity in both reactions. Reducing agents increased photophosphorylation activity of aromatic pteridines and an oxidant increased activity of a tetrahydropteridine. It is postulated that pteridines are most active in their semiquinone or unstable dihydro forms.

Chloroplasts↗
PubMed1966

Reduction of nitrate and nitrite by subcellular preparations of Anabaena cylindrica. I. Reduction of nitrite to ammonia.

Reduction of nitrite by cell-free preparations of Anabaena cylindrica in the dark has been investigated. Nitrite-reducing activity was recovered in a supernatant fraction. The nitrite reductase system was partially purified by column chromatography on Sephadex G-75. NADPH could serve as an H-donor. NADH was completely inactive. The reduction required ferredoxin which mediated the transfer of electrons from NADPH to nitrite. Ferredoxin was successfully replaced with methyl viologen, benzyl viologen and diquat. The nitrite-reducing activity was inhibited by KCN, and by 2,4-dinitrophenol and arsenate at higher concentrations. The extent of nitrite reduction by NADPH was dependent on the oxidation-reduction states of NADP and ferredoxin.

Eukaryota↗
PubMed1964

Use of algae for support of the human in space.

Algae offer special advantages as photosynthetic plants which may be used to provide for the gas exchange requirements of man and for some fraction of his food requirement. Established principles of algal metabolism allow basic specifications. To meet a human oxygen demand of 600 1/day an algal exchanger would take up about 720 1/day of carbon dioxide, produce about 600 g/day of dry algae, and require a minimum of about 800 watt of visible light. Major technical disadvantage arises from need for input power as light and the low values of irradiance at which algae can maintain maximum efficiency. Design criteria require compromise between minimum volume and minimum power requirement. A basic design theory needs to be evolved and a number of technical problems need to be solved before proper evaluation of an algal system can be made.

Carbon Dioxide↗