Twenty-four-hour variations in activity,core temperature,metabolic rate,and respiratory quotient in captive chinese pangolins

The circadian rhythms in activity, core temperature (T_c), O₂ consumption, CO₂ production, and respiratory quotient (RQ) were monitored in four captive Chinese pangolins (Manis pentadactyla). The pangolins were strictly nocturnal, never emerging from their nest before 1600 h, and their intermittent activity continued no later than 0230. As is usual in nocturnal mammals, the highest values observed in T_c, O₂ consumption, and CO₂ production occurred during the night; the lowest values occurred during the day. The magnitude of the variation in T_c, O₂ consumption, CO₂ production, and RQ averaged 1.2°C, 1.3 ml O₂ kg^?1 min^?1, 1.2 ml CO₂ kg^?1 min^?1, and 0.24, respectively. The circadian pattern in RQ was independent of activity, T_c, and the metabolic parameters and was of a different character than the patterns exhibited in the other variables. RQ remained constant at either a high or low level for long periods (8–10 h) and then increased or decreased relatively rapidly (1–2h) to the other level as in a square wave, whereas the rhythms in the other variables are similar to sine waves. The sharp increase in RQ was followed by a slow decline in T_c, and the sharp decline in RQ was followed by a slow increase in T_c.     

Succinate metabolism related to lipid synthesis in the housefly Musca domestica L

The metabolism of succinate was examined in the housefly Musca domestica L. The labeled carbons from [2,3-¹⁴C]succinate were readily incorporated into cuticular hydrocarbon and internal lipid, whereas radioactivity from [1,4-¹⁴C]succinate was not incorporated into either fraction. Examination of the incorporation of [2,3-¹⁴C]succinate, [1-¹⁴C]acetate, and [U-¹⁴C]proline into hydrocarbon by radio-gas-liquid chromatography showed that each substrate gave a similar labeling pattern, which suggested that succinate and proline were converted to acetyl-CoA prior to incorporation into hydrocarbons. Carbon-13 nuclear magnetic resonance showed that the labeled carbons from [2,3-¹³C]succinate enriched carbons 1, 2, and 3 of hydrocarbons with carbon-carbon coupling showing that carbons 2 and 3 of succinate were incorporated as an intact unit. Radio-high-performance liquid chromatographic analysis of [2,3-¹⁴C]succinate metabolism by mitochondrial preparations showed that in addition to labeling fumarate, malate, and citrate, considerable radioactivity was also present in the acetate fraction. The data show that succinate was not converted to methylmalonate and did not label hydrocarbon via a methylmalonyl derivative. Malic enzyme was assayed in sonicated mitochondria prepared from the abdomens and thoraces of 1- and 4-day-old insects; higher activity was obtained with NAD⁺ in mitochondria prepared from thoraces, whereas NADP⁺ gave higher activity with abdomen preparations. These data document the metabolism of succinate to acetyl-CoA and not to a methylmalonyl unit prior to incorporation into lipid in the housefly and establish the role of the malic enzyme in this process.     

The metabolism of deoxyguanosine in mitochondria. Characterization of the uptake process

Summary The uptake of deoxyguanosine by rat liver mitochondria was characterized. The process required an intact mitochondrial membrane and exhibited a dependence on added phosphate. Deoxyguanosine uptake was minimally influenced by Mg²⁺ or Mn²⁺, but Ca²⁺ at concentrations above 0.5 mM were detrimental. Of the deoxynucleosides tested, only deoxyinosine inhibited the uptake of deoxyguanosine. The ribonucleoside guanosine was not observed to compete with its deoxynucleoside analog. Known inhibitors of nucleoside transport, cytochalasin B and NBMPR, did not block deoxyguanosine uptake, but the sulfhydryl reagents NEM and pCMB were both inhibitory. The uptake of deoxyguanosine was shown to be a saturable process and an apparent Km of 0.64 M was calculated from a Hanes plot.     

Glucose and amino acid metabolism in chick telencephalon slices: Changes with incubation conditions and animals' development

Glucose and amino acid metabolism in 1- and 30-day-old chick telencephalon slices was studied in two incubation media in the presence or in the absence of a continuous oxygenation. Medium 1 has a composition and a tonicity similar to cerebrospinal fluid, medium 2 is hypertonic and does not contain any K⁺ ions. The incorporation of glucose carbon into amino acids and the distribution of radioactivity between the different amino acids are close to the ones observed in the chick brain in vivo only when the slices are incubated in medium 1, with oxygen at 30 days and without oxygen for the 1-day-old chick. It also appears that if oxygenation is necessary for incubation of mature brain tissue in vitro, the absence of the medium oxygenation is more suitable for the study of glucose metabolism in 1-day-old chick brain slices.     

Properties of the 3′-phosphoadenosine-5′-phosphosulfate (PAPS) synthesizing systems of brain and liver

Chromatography of brain and liver 100,000g supernatants over HPLC molecular sieve columns revealed striking differences in the molecular weight distribution of ATP-sulfurylase and APS-kinase of the two tissues, pointing to different enzymic species for both enzymes in brain and liver. This was further substantiated by kinetic characterization of the two enzymes of both tissues. APS-kinase of liver is allosterically activated by ATP, while the brain enzyme is not. ATP-sulfurylase of brain is activated at high, but still physiological concentrations of ATP. Brain ATP-sulfurylase is inhibited by phenylalanine.     

Phenobarbital and 6-aminonicotinamide effect on cerebral enzymatic activities related to energy metabolism in different rat brain areas

The effect of phenobarbital (100 mg/kg i.p.) and 6-aminonicotinamide (6AN) (35 mg/kg i.p.) on enzyme activities related to energy transduction was investigated on the homogenate in toto, non-synaptic mitochondrial fraction and synaptosomal fraction isolated from different rat brain areas (cerebral cortex, hippocampus, hypothalamus, striatum, and medulla oblongata). 6AN treatment decreased: (a) phosphofructokinase in all the areas tested; (b) lactate dehydrogenase on the homogenate in toto in striatum and hypothalamus, and on the synaptosomal fraction in cerebral cortex and corpus striatum; (c) succinate dehydrogenase on non-synaptic mitochondrial fraction in hippocampus and striatum. Finally, aspartate aminotransferase was increased on non-synaptic mitochondrial fraction in striatum and medulla oblongata. Phenobarbital treatment induced an increase of total NADH cytochrome c reductase on mitochondrial fraction in hippocampus and hypothalamus, and a decrease of cytochrome oxidase activity on non-synaptic mitochondrial fraction in hypothalamus and medulla oblongata.     

Long-term support by injured brain extract of a subpopulation of ciliary ganglion neurons purified by differential adhesion

Ciliary ganglion neurons and nonneurons can be separated from each other, based on the greater adhesivity of the nonneurons to untreated tissue culture plastic in the presence of serum. When the separation was carried out in the presence of Serum Plus (a commercially available supplemented serum), two populations of neurons were distinguished. Neurons in the first class (50–60% of total) adhered to plastic within 15 min, tended to aggregate into clumps, and were not well supported in long term culture by brain extracts. Neuronal adhesion to plastic was inhibited by heparin but not by chondroitin sulfate. Neurons in the second class did not attach to plastic for up to 90 min (and could thus be purified), were not as prone to aggregation, and were quantitatively supported for long periods (>2 weeks) by the neurotrophic factor(s) present in extracts of injured brain. Although no direct evidence is provided, these populations may correspond to the well characterized ciliary and choroid neurons.Special Issue dedicated to Dr. E. M. Shooter and Dr. S. Varon.     

Chick brain glutamine synthetase and Mn2+−Mg2+ interactions

Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg²⁺ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca²⁺, Co²⁺, Fe²⁺, Li⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺) only Co²⁺, Mg²⁺ and Mn²⁺ supported GS activity; the order of activatory ability was Mg²⁺>Co²⁺>Mn²⁺. The maximum activating effect of Mn²⁺ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn²⁺, modulates the Mg²⁺ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis.     

Na+−K+-ATPase activity of glial,neuronal, and synaptosomal enriched fractions from normal and freezing-injured rabbit cerebral cortex

This paper investigates the kinetic parameters of Na⁺–K⁺-ATPase in glial, neuronal, and synaptosomal enriched fractions isolated from rabbit cerebral cortex. Under normal conditions, kinetic parameters-V_max and K _0.5 ^K+ -of Na⁺–K⁺-ATPase are the same in the three fractions, suggesting that this enzyme behaves as the same molecular entity. Following a cryogenic lesion, the alterations of these parameters appear to be different in the different fractions. These data suggest that the same enzyme exhibits various responses when exposed to the same pathological event. The dissimilar lipid composition of the Na⁺–K⁺-ATPase environment, and/or different adaptative responses to abnormal ion concentrations in glial, neuronal, and synaptosomal fractions could account for these different responses.     

Nuclear-magnetic-resonance imaging of leaves ofMesembryanthemum crystallinum L. plants grown at high salinity

Differences in water binding were measured in the leaf cells ofMesembryanthemum crystallinum L. plants grown under high-salinity conditions by using nuclear-magnetic-resonance (NMR) imaging. The 7-Tesla proton NMR imaging system yielded a spatial resolution of 20·20·100 m³. Images recorded with different spin-echo times (4.4 ms to 18 ms) showed that the water concentrations in the bladder cells (located on the upper and lower leaf surface), in the mesophyll cells and in the water-conducting vessels were nearly identical. All of the water in the bladder cells and in the water-conducting vessels was found to be mobile, whilst part of the water in the mesophyll cells was bound. Patches of mesophyll cells could be identified which bound water more strongly than the surrounding mesophyll cells. Optical investigations of leaf cross-sections revealed two types of mesophyll cells of different sizes and chloroplast contents. It is therefore likely that in the small-sized mesophyll cells water is strongly bound. A long-term asymmetric water exchange between the mesophyll cells and the bladder cells during Crassulacean acid metabolism has been described in the literature. The high density of these mesophyll cells in the lower epidermis is a possible cause of this asymmetry.Abbreviations CAM Crassulacean acid metabolism - NMR nuclear magnetic resonance - T_E spin-echo time