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61.
Changes in the activity of 6-phosphofructo-1-kinase (PFK, EC 2.7.1.11) from the epithelial cells of rat small intestine during experimental hypothyroidism were studied. Hypothyroidism resulted in significant decreases in the plasma concentrations of total tri-iodothyronine, free tri-iodothyronine, total thyroxine, free thyroxine and insulin. These changes were associated with a significant increase in the plasma concentration of thyrotropin. The total activity and activity ratios (activity at 0.5 mM fructose 6-phosphate at pH 7.0/activity at pH 8.0 (v0.5/V)) of jejunal PFK of hypothyroid rats were significantly diminished as compared to control rats. PFK of hypothyroid rats was more sensitive to inhibition by ATP. The mucosal enzyme of both control and hypothyroid state was sensitive to stimulation by AMP and fructose 2,6-bisphosphate. It is concluded that during hypothyroidism the rate of glycolytic pathway in the small intestine is reduced as a result of a fall in glucose uptake, and the subsequent kinetic changes of PFK are primarily to maintain the concentrations of fructose 6-phosphate (and glucose 6-phosphate) during the reduced glycolytic flux. These changes in PFK activity may be caused by changes in plasma insulin concentrations, glucose utilization and fructose 2,6-bisphosphate concentrations. 相似文献
62.
Adolf Seilacher Sebastian Lü ning Mike A. Martin Eberhard Klitzsch Abdallah Khoja Jonathan Craig 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2002,35(3):257-262
The Lower Palaeozoic deposits in North Africa are dominated by sandstones and shales which often lack biostratigraphically useful body fossils. Trilobite burrows ( Cruziana ) partly fill this gap and provide the basis for medium-resolution stratigraphic interpretations. Several Ordovician-Silurian ichnostratigraphically significant Cruziana forms have been found and studied in the Kufra Basin (SE Libya), including C. goldfussi and C. furcifera from the Lower Ordovician Hawaz Fm. and a new ichnospecies, C. kufraensis , occurring in transgressive sandstones at the base of the Lower Silurian Tanezzuft Fm. The upper Tanezzuft Fm. and Akakus Fm. typically contain C. acacensis , a form that is characteristic of the Lower Silurian of Northern Gondwana. 相似文献
63.
Ruchira Chatterjee Louise Lassalle Sheraz Gul Franklin D. Fuller Iris D. Young Mohamed Ibrahim Casper de Lichtenberg Mun Hon Cheah Athina Zouni Johannes Messinger Vittal K. Yachandra Jan Kern Junko Yano 《Physiologia plantarum》2019,166(1):60-72
In nature, an oxo‐bridged Mn4CaO5 cluster embedded in photosystem II (PSII), a membrane‐bound multi‐subunit pigment protein complex, catalyzes the water oxidation reaction that is driven by light‐induced charge separations in the reaction center of PSII. The Mn4CaO5 cluster accumulates four oxidizing equivalents to enable the four‐electron four‐proton catalysis of two water molecules to one dioxygen molecule and cycles through five intermediate S‐states, S0 – S4 in the Kok cycle. One important question related to the catalytic mechanism of the oxygen‐evolving complex (OEC) that remains is, whether structural isomers are present in some of the intermediate S‐states and if such equilibria are essential for the mechanism of the O‐O bond formation. Here we compare results from electron paramagnetic resonance (EPR) and X‐ray absorption spectroscopy (XAS) obtained at cryogenic temperatures for the S2 state of PSII with structural data collected of the S1, S2 and S3 states by serial crystallography at neutral pH (~6.5) using an X‐ray free electron laser at room temperature. While the cryogenic data show the presence of at least two structural forms of the S2 state, the room temperature crystallography data can be well‐described by just one S2 structure. We discuss the deviating results and outline experimental strategies for clarifying this mechanistically important question. 相似文献