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Photosynthesis

Description: The overall process of photosynthesis involves a number of interconnected processes. These processes, which are cyclic with respect to both energy and material, are related at some points to well-known respiratory processes. The carbon-reduction cycle in photosynthesis is now known in detail. All enzymes involved in this cycle have been isolated and the sources of energy required for its operation have been identified in terms of reducing agents and 'high-energy' phosphate. These sources of energy a r e derived ultimately from absorbed light energy which brings about the photolysis of water. Possible mechanisms for this photolysis and for the transfer of energy from the photolysis products to the carbon-reduction cycle are discussed here. Experimental data, in the form of quantum efficiency measurements, are presented and partially confirm the theories proposed for the mechanisms of energy transfer. A diagram of the complete process of photosynthesis containing the several cycles and their relations is presented.
Date: February 1, 1955
Creator: Bassham, James A. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Sites of Azaserine Inhibition During Photosynthesis byScenedesmus

Description: The success attending the use of azaserine as a specific inhibitor of one atage in the metabolic pathway leading to the synthesis of inosinic acid in pigeon liver prompted us to use this antibiotic in a similar attack on purine synthesis in Scenedesmus. However, investigation of the products produced during photosynthesis by suspensions of these algae in the presence of azaserine showed that a more widespread interference with metabolism had occurred. The purpose of this communication is to describe the nature of these effects and to attempt to assess their importance in a general picture of the metabolic effects of azaserine.
Date: May 8, 1956
Creator: Barker, S. Alan; Bassham, James A.; Calvin, M. & Quarck, Ursula C.
Partner: UNT Libraries Government Documents Department

The Relation of Quantum Requirement in Photosynthesis toRespiration

Description: 1. The r a t e s of photosynthesis and subsequent respiration of Chlorella pyrenoidosa were measured using an oxygen analyzer (sensitive to paramagnetism). The energy absorbed during the photosynthesis periods was determined and the quantum requirement was calculated. 2. Dark respiration r a t e was found to depend on the r a t e of light absorption during the period of photosynthesis, and increased with increasing photosynthesis rate. 3 . The quantum requirement, corrected for respiration, varied from 4. 9 ( a t a ratio of photosynthesis to respiration of 1.4) to 6. 9 (at a r a t i o of 12). Both uncorrected and corrected quantum requirements approach an experimental value of 7. 4 a t high light intensity. 4. The lower quantum requirement obtained a t low light intensity is believed to be due to a relatively greater importance of contribution of energy from respiration t o photosynthesis. An expression i s derived for the relation between this contribution and the enhancement of dark respiration due to the level of photosynthesis to which the plants a r e conditioned. 5. Attempts to obtain the blue -light stimulation of photosynthesis with algae photosynthesizing in r e d light were unsuccessful.
Date: January 21, 1955
Creator: Bassham, James A.; Shibata, Kazuo & Calvin, M.
Partner: UNT Libraries Government Documents Department

The Path of Carbon in Photosynthesis VIII. The Role of MalicAcid

Description: Malonate has been found to inhibit the formation of malic acid during short periods of photosynthesis with radioactive carbon dioxide. This result, together with studies which show the photosynthetic cycle to be operating normally at the same time, indicates that malic acid is not an intermediate in photosynthesis but is probably closely related to some intermediate of the cycle. Absence of labeled succinic and fumaric acids in these experiments, in addition to the failure of malonate to inhibit photosynthesis, precludes the participation of these acids as intermediates in photosynthesis.
Date: January 25, 1950
Creator: Bassham, James A.; Benson, Andrew A. & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

The Photosynthetic Cycle and Respiration: Ligh-DarkTransients

Description: Studies of the transient changes in radiocarbon found in various photosynthetic and respiratory intermediates in Scenedesmus, which result when changing from a condition of steady-state photosynthesis in the light to dark and then back to light again, indicate the following metabolic mechanisms: (a) The carboxylation step in the carbon-reduction cycle of photosynthesis results in the formation of two molecules of 3-PGA from one RuDP molecule, one CO{sub 2}, and one H{sub 2}O: (b) This carboxylation reaction proceeds for about thirty seconds in the dark after the light is turned off and its rate is proportional to the falling concentration of RuDP, and stops when the latter concentration falls to zero. (c) Turning off the light results in the transfer of radiocarbon from PGA to citric acid, and glutamic acid, whereas turning on the light results in a decrease in radiocarbon in citric acid. These results provide new evidence for the theory that the oxidation of pyruvic acid to acetyl CoA and CO{sub 2} with a subsequent condensation of acetyl CoA with oxaloacetic acid to give citric acid is blocked in the light by reduction of a cofactor, which may be thioctic acid, required for pyruvic acid oxidation. (d) These transients in radioactivity found in Krebs-cycle acids are taken as evidence for the association with the chloroplast of enzymes and intermediates of the Krebs cycle.
Date: March 1, 1956
Creator: Bassham, James A.; Shibata, Kazuo; Steenberg, Kjell; Bourdon,Jean & Calvin, M.
Partner: UNT Libraries Government Documents Department

AMINO ACID SYNTHESIS IN PHOTO-SYNTHESIZING SPINACH CELLS. EFFECTS OF AMMONIA ON POOL SIZES AND RATES OF LABELING FROM {sup 14}CO{sub 2}

Description: Isolated cells from leaves of Spinacea oleracea have been maintained in a state capable of high rates of photosynthetic CO{sub 2} fixation for more than 60 h. The incorporation of {sup 14}CO{sub 2} under saturating CO{sub 2} conditions into carbohydrates, carboxylic acids, and amino acids, and the effect of ammonia on this incorporation have been studied. Total incorporation, specific radioactivity and pool size have been determined as a function of time for most of the protein amino acids and for {gamma}-aminobutyric acid. the measurements of specific activities and of the approaches to {sup 14}C "saturation" of some amino acids indicate the presence and relative sizes of metabolically active and passive pools of these amino acids. Added ammonia decreased carbon fixation into carbohydrates and increased fixation into carboxylic acids and amino acids. Different amino acids were, however, affected in different and highly specific ways. Ammonia caused large stimulatory effects in incorporation of {sup 14}C into glutamine (a factor of 16), No effect or slight decreases were seen in glycine, serine, phenylalanine, and tyrosine labeling, In.the case of glutamate, {sup 14}C-labeling decreased, but specific activity increased. The production of labeled {gamma}-aminobutyric acid was virtually stopped by ammonia. The results indicate that added ammonia stimulates the reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase, as seen with other plant systems. The data on the effects of added ammonia on total labeling, pool sizes, and specific activities of several amino acids provides a number of indications about the intracellular sites of principal synthesis from carbon skeletons of these amino acids and the selective nature of effects of increased intracellular ammonia concentration on such synthesis.
Date: October 1, 1980
Creator: Larsen, Peder Olesen; Cornwell, Karen L.; Gee, Sherry L. & Bassham, James A.
Partner: UNT Libraries Government Documents Department