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Biomedical subjects

J Myers

Publications and source records attributed to J Myers.

At least 271 records · Page 15Linked to original sources
PubMed1971

The Kok Effect in Chlamydomonas reinhardi.

A Haxo-Blinks rate-measuring oxygen electrode together with a modulated light source gave an average current signal (change in net O(2) exchange) and a modulated current signal (photosynthetic O(2) evolution). Using this apparatus, net O(2) exchange and photosynthetic O(2) evolution at low intensities have been studied in the green alga, Chlamydomonas reinhardi. At both 645 nm and 695 nm, the curves of net O(2) exchange as a function of light intensity were steeper at lowest intensities than about compensation, indicative of the Kok effect. The effect was greater at 695 nm than at 645 nm. The corresponding curves of photosynthetic O(2) evolution, on the other hand, showed no Kok effect; here, the slope was lowest at lowest intensity. The absence of the Kok effect in O(2) evolution, together with its sensitivity to monofluoroacetic acid, show that it is due to an interaction of photosynthesis and respiration. The effect was exaggerated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In the presence of concentrations of this inhibitor sufficient to inhibit O(2) evolution completely, a light-induced change in net O(2) exchange remained. This was interpreted as a system I dependent depression of respiratory O(2) uptake. The Kok effect remained undiminished in concentrations of carbonyl cyanide m-chlorophenylhydrazone and 2,4-dinitrophenol which partially uncoupled either oxidative phosphorylation alone or both oxidative and photosynthetic phosphorylations. The above results can be explained within a model of the Kok effect in which O(2) uptake is depressed by diversion of reductant away from respiratory electron transport and into photosystem I. The same photodepression of O(2) uptake also appears to account for a transient in net O(2) exchange seen in several algae upon turning off the light.

Journal Article↗
PubMed1971

The photosynthetic unit in chlorella measured by repetitive short flashes.

Apparent size of the photosynthetic unit in Chlorella pyrenoidosa was estimated by the method of Emerson and Arnold: rate of oxygen evolution was measured under repetitive saturating flashes of about 10-microsecond duration separated by dark periods of 0.033 to 0.100 second. Cells used were taken from six steady state cultures maintained at different light intensities. Cell characteristics included a variation in chlorophyll content from 1 to 5%. Apparent size of the photosynthetic unit varied systematically with chlorophyll content in the range of 1560 to 2350 chlorophylls per O(2) per flash. Values for unit size showed no unusual statistical distribution and were not changed significantly by addition of low level background light at 645 or 705 nanometers. Maximal rate of unit turnover, calculated from light-saturated rate and unit size, varied inversely with chlorophyll content in the range of 70 to 180 per second.

Journal Article↗
PubMed1968

Photosynthetic Enhancement in the Diatom Phaeodactylum tricornutum.

Enhancement phenomena in photosynthesis of the diatom Phaeodactylum tricornutum Lewin were studied by means of a Haxo oxygen electrode and 2 monochromatic light beams. It was necessary to correct for a minor non-linearity in rate oxygen evolution vs. intensity similar to that reported for Chlorella. Action spectra on complementary backgrounds and derived enhancement spectra were compared to in vivo absorption spectra in identifying the character of pigment systems 1 and 2. Fucoxanthin, chlorophyll c, and chlorophyll a-670 are clearly assignable to pigment system 2 which absorbs in excess at wavelengths 400 to 678 mmu. Chlorophyll a-1 (and a portion of the fucoxanthin) are assignable to pigment system 1 which absorbs in excess at wavelengths 678 to 750 mmu. Enhancement values were generally lower than those observed in Chlorella or Anacystis and lead to conclusion that diatom pigmentation provides an effective light harvesting apparatus.

Journal Article↗
PubMed1967

Enhancement of photosynthesis by alternated light beams and a kinetic model.

Using the alga Chlorella and 2 light beams of defined wavelength, we have found that short period (1 sec) alternation gives all characteristics of enhancement of net oxygen evolution observed when the beams are superimposed. With increasing period of alternation (1-20 see) decay in enhancement is more rapid at higher intensities. We have developed a kinetic model for the current hypothesis of 2 photoacts operating in series and separated by electron transport reactions. The model is applicable at low light intensity such that rate is governed only by intensities and the fractions of reaction centers open for each photoact. Potentials and pool sizes of intermediates were taken from current estimates. Wavelength dependency of the 2 photoacts was taken from enhancement spectra for superimposed light beams. Analog computer treatment of the kinetic equations gave predictions of chromatic transients and alternated enhancement which are in reasonable but not complete agreement with experimental observations.

Chemical Phenomena↗