Abstract: Local cerebral glucose utilization was measured by the [14C]2-deoxy- d -glucose method in conscious control and hyperketonemic rats. Hyperketonemia was induced by 3 days of starvation or by infusion of 3- hydroxybutyrate in fed rats. These treatments produced combined blood ketone body concentrations (acetoacetate + 3-hydroxybutyrate) of from 1.2 to 2.4 mM. Neither treatment significantly affected glucose utilization in any of the 15 brain regions studied. These observations indicate that hyperketonemia in resting, conscious rats does not interfere with brain uptake and phosphorylation of glucose. 相似文献
A mathematical model of protoplasmic streaming in a plant cell such as Nitella and Chara is studied. General rheological equations for the non-Newtonian fluid is derived theoretically, and the boundary value problem for the model is solved. The pattern of motion of cytoplasm in a living cell is obtained, and the rheological property of protoplasm is evaluated in vivo. 相似文献
1. 1. The relationship between temperature and Hill reaction activity has been investigated in chloroplasts isolated from barley (Hordeum vulgare L. cv. Abyssinian).
2. 2. An Arrhenius plot of the photoreduction of 2,6-dichlorophenolindophenol (DCIP) showed no change in slope over the temperature range 2–38 °C. The apparent Arrhenius activation energy (Ea) for the reaction was 48.1 kJ/mol.
3. 3. In the presence of an uncoupler of photophosphorylation, methylamine, the Ea for DCIP photoreduction went through a series of changes as the temperature was increased. Changes were found at 9, 20, 29 and 36 °C. The Ea was highest below 9 °C at 63.7 kJ/mol. Between 9 and 20 °C the Ea decreased to 40.4 kJ/mol and again to 20.2 kJ/mol between 20 and 29 °C. Between 29 and 36 °C there was no further increase in activity with increasing temperature. The temperature-induced changes at 9, 20 and 29 °C were reversible. At temperatures above 36 °C (2 min) a thermal and largely irreversible inactivation of the Hill reaction occurred.
4. 4. Temperature-induced changes in Ea were also found when ferricyanide was substituted for DCIP or gramicidin D for methylamine. The addition of an uncoupler of photophosphorylation was not required to demonstrate temperature-induced changes in DCIP photoreduction following the exposure of the chloroplasts to a low concentration of cations.
5. 5. The photoreduction of the lipophilic acceptor, oxidized 2, 3, 5, 6-tetramethyl-p-phenylenediamine, also showed changes in Ea in the absence of an uncoupler.
6. 6. The temperature-induced changes in Hill activity at 9 and 29 °C coincided with temperature-induced changes in the fluidity of chloroplast thylakoid membranes as detected by measurements of electron spin resonance spectra. It is suggested that the temperature-induced changes in the properties and activity of chloroplast membranes are part of a control mechanism for regulation of chloroplast development and photosynthesis by temperature.
SYNOPSIS. A reduction in the growth temperature of Tetrahymena pyriformis strain WH-14 from 35 C to 15 C resulted in distinct alterations in the fatty acid composition of the glycerophospholipids. The proportion of normal saturated acids declined from 26 to 19%; palmitoleic acid increased by 6%, and the composition of the polyunsaturated fatty acids increased in 18:2 Δ6,11(n) and decreased in 18:2 Δ9,12(n) and 18:3 Δ6,9,12(n). The unsaturation index (the average number of double bonds/100 molecules) did not change with a shift in temperature. Two biosynthetic pathways exist in Tetrahymena for the formation of unsaturated fatty acids. The observed changes in fatty acid composition that accompany a lowering of the environmental temperature can be accounted for by a reduction in the accumulation of products of the fatty acid pathway leading to the formation of γ-linolenic acid [16:0(n) → 18:0(n) → 18:1 Δ9(n) → 18:2 Δ9,12(n) → 18:3 Δ6,9,12(n)] and an increase in the components of the pathway leading to the formation of 18:2 Δ6,11(n) [16:0(n) → 16:1 Δ9(n) → 18:1 Δ11(n) → 18:2 Δ6,11(n)]. The data suggest that the regulatory mechanism in Tetrahymena differs from that found in some bacteria where a simple substitution of unsaturated fatty acids for saturated fatty acids occurs at low culture temperatures. 相似文献
Incubations of testes of adult rats with testosterone yield rather important amounts of a very polar metabolite which is identified as 7α-hydroxytestosterone. The identification of the metabolite is based on chromatography, spectrophotometry, fluorimetry, counter current distribution and NMR spectrometry. 相似文献
An improved method for detecting four Np-1 (purine nucleoside phosphorylase) alleles in mouse erythrocytes by cellulose acetate electrophoresis is described. The previous linkage of Np-1 and Es-10 (esterase-10) was confirmed, with a map distance of 13.0±2.6 cM. Np-2 was detected by either specific activity assay or starch gel electrophoresis and shown to be linked to Es-10, 15.9 ± 3.1 cM, on chromosome 14. No recombinants between Np-1 and Np-2 were observed in 52 offspring, indicating either that these loci are either closely associated or that Np-2 represents simply a property of existing allelic products of the Np-1 locus.This research was supported by Medical Research Council of Canada grants to F.G.B. and F.F.S. 相似文献
The effect of the bacterial cytolytic toxin, streptolysin S, on liposomes composed of various phospholipids was investigated. Large unilamellar vesicles containing [14C]sucrose were prepared by reverse-phase evaporation, and membrane damage produced by the toxin was measured by following the release of labeled marker. The net charge of the liposomes had little or no effect on their susceptibility to steptolysin S and the toxin was about equally effective on liposomes composed of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylglycerol. Experiments with liposomes composed of synthetic phospholipids showed that the ability of the toxin to produce membrane damage depended on the degree of unsaturation of the fatty acyl chains. The order of sensitivity was C18 : 2 phosphatidylcholine > C18 : 1 phosphatidylcholine > C18 : 0 phosphatidylcholine = C16 : 0 phosphatidylcholine. Liposomes containing the latter two phospholipids were virtually unaffected by streptolysin S, and experiments with C18 : 0 phosphatidylcholine suggested that toxin activity does not bind to liposomes composed of phospholipids with saturated fatty acyl chains. The inclusion of 40 mol% cholesterol in C16 : 0 phosphatidylcholine and C18 : 0 phosphatidylcholine liposomes made these vesicles sensitive to streptolysin S. Egg phosphatidylcholine liposomes, which were unaffected at 0°C and 4°C became susceptible to the toxin at these temperatures when cholesterol was included. Liposomes composed of C14 : 0 phosphatidylcholine were unaffected by streptolysin S at temperatures below the chain-melting transition temperature (23°C) of this phospholipid, but became increasingly susceptible above this temperature. The results suggest that the fluidity of the phospholipid hydrocarbon chains in the membrane is important in streptolysin S action. 相似文献