Purine metabolism in cotyledons and embryonic axes of black gram (Phaseolus mungo L.) Seedlings

• 1.1. The metabolism of purine bases and nucleosides in cotyledons and embryonic axes of black gram (Phaseolus mungo L.) was studied.
• 2.2. A large portion of absorbed [8-¹⁴C]adenine, [8-¹⁴C]guanine and [8-¹⁴C]adenosine was salvaged in nucleotide and nucleic acid synthesis.
• 3.3. Most of the radioactivity of [8-¹⁴C]hypoxanthine and [8-¹⁴C]inosine was incorporated into allantoin and allantoic acid.
• 4.4. Activity of adenine phosphoribosyltransferase in enzyme extracts was much higher than that of hypoxanthme and guanine phosphoribosyltransferase(s).
• 5.5. Apparent activity of adenosine kinase was higher than that of inosine kinase. 6. NAD⁺-dependent xan thine dehydrogenase was detected in both cotyledons and embryonic axes of the seedlings.
• 6.7. The capacity of purine salvage was higher m 24 hr old cotyledons than 24 and 48 hr old embryonic axes. The reverse was observed concerning that of purine degradation.

     

In vitro substrate utilization for lipid synthesis in liver explants from hyperthyroid chickens

• 1.1. Indian River male broiler chickens growing from 7 to 28 days of age were fed diets containing 12, 18, 24 and 30% protein + 0 or 1 mg triiodothyronine (T₃)/kg of diet to study energetic costs of lipogenesis and the use of various substrates for in vitro lipogenesis.
• 2.2. De novo lipid and CO₂ production were determined in the presence of [1-¹⁴C]pyruvate, [2-¹⁴q]pyruvate, [3-¹⁴C]pyruvate, [2-¹⁴C]acetate and [U-¹⁴C]alanine.
• 3.3. Oxygen consumption was determined in mitochondrial preparations to estimate the energetic costs in expiants synthesizing lipid.
• 4.4. Radiolabeled CO₂ derived from [1-¹⁴C]pyruvate was used as an estimate of coenzyme A availability in liver expiants. Lipids derived from [2-¹⁴C]pyruvate, [2-¹⁴C]acetate and [U-¹⁴C]alanine estimate relative substrate efficiency.
• 5.5. Labeled CO₂ production from [1-¹⁴C]pyruvate was greatest in that group fed a 12% protein diet and least in the group fed a 30% protein diet.
• 6.6. In addition, T₃ increased CO₂ production from [1-¹⁴C]pyruvate.
• 7.7. The production of ¹⁴CO₂ from the second carbon of pyruvate or acetate was increased by T₃.
• 8.8. The low-protein diet (12% protein) increased (P <0.05) lipogenesis.
• 9.9. Adding T₃ to the diets decreased carbon flux into lipid from all substrates, but increased CO₂ production from all substrates without changing stage 3 and 4 respiration rates in mitochondrial preparations.
• 10.10. These observations imply that coenzyme A availability may have regulated de novo lipogenesis in the present study.
• 11.11. It was also concluded that previously noted effects of T₃ on intermediary metabolism may involve metabolic pathways that do not involve changes in mitochondrial function.

     

Fetal lung metabolism: Response to maternal fasting

• 1.1. Fetal lung metabolic response to maternal fasting late in gestation was investigated.
• 2.2. Maternal fasting 4 days before term was associated with low fetal plasma glucose and insulin levels but increased levels of fetal plasma glucagon, glycerol, lactate and fatty acids.
• 3.3. Fetuses from fasted mothers showed a significant decrease in body weight (30%), lung weight (30%) and lung glycogen (46%), but no change in lung protein, phospholipid or total lung DNA, suggesting that lung size is affected more than maturation.
• 4.4. Fetal lung slices incubated in vitro showed that lactate oxidation to CO₂ equalled that of glucose in control fetal lungs and was unaffected by maternal fasting, while glucose oxidation was depressed (23%).
• 5.5. Maternal fasting significantly decreased in vitro incorporation of [U-¹⁴C]-glucose, [U-¹⁴C]lactate and [1-¹⁴C]palmitate into lung phospholipids.
• 6.6. Fetal lungs from fasted mothers showed increased conversion of lactate to glucose, indicating gluconeogenic potential by fetal lung.
• 7.7. These studies show that plasma lactate serves as an important energy fuel and substrate for lipid synthesis for the fetal lung, and maternal fasting markedly alters fetal lung metabolism.

     

Amino acid synthesis during hyperosmotic stress in penaeus aztecus postlarvae

• 1.1. Glycine, proline, and taurine are the quantitatively most important amino acid osmolytes in Penaeus aztecus postlarvae.
• 2.2. Taurine dominates the amino acid pool in low salinity, while proline dominates the amino acid pool at higher salinities.
• 3.3. Although not major contributors to the pool, glutamate and alanine are constitutively synthesized from [¹⁴C]glucose and [¹⁴C]glutamate under constant salinity and under hyperosmotic stress treatments.
• 4.4. Proline synthesis from [¹⁴C]-precursors is apparent under constant high (but not low) salinity and is significantly induced by hyperosmotic stress.
• 5.5. No appreciable glycine synthesis was observed from [¹⁴C]glucose or [¹⁴C]glutamate under any experimental conditions.

     

Possible involvement of adenylylation in the modification of a 26 kDa protein in rat parotid acinar cells

• 1.1. Adenylylation, a posttranslational modification of proteins, was investigated in saponin-permeabilized acinar cells of the rat parotid gland.
• 2.2. When cells were incubated with [2,8-³H]ATP, several proteins, including a 26 kDa protein in the particulate fraction, were labeled.
• 3.3. Upon incubation of cells with [α-³²P]ATP in the presence of cAMP and 3-isobutyl-lmethylxanthine, ³²P-labeling of the 26 kDa protein was observed.
• 4.4. After treatment with snake venom phosphodiesterase, [³²P]AMP was released from the 26kDa protein. Such release was not observed when cells were labeled with [γ-³²P]ATP.
• 5.5. The ³²P-labeling pattern of proteins with [α-³²P]ATP was clearly different from that with [adenylate-³²P]NAD⁺.
• 6.6. The results suggest that the 26 kDa protein is one of the adenylylation substrates in rat parotid acinar cells.

     

Synthesis of reserved polysaccharide from wax esters accumulated as the result of anaerobic energy generation in Euglena gracilis returned from anaerobic to aerobic conditions

• 1.1. Euglena gracilis SM-ZK (a non-photosynthetic mutant), cultured in Koren-Hutner medium, containing glucose, malate and glutamate as the main nutrients, were incubated anaerobiosis for 24 hr, and then returned to aerobic conditions. Wax esters, which were synthesized from paramylon (the reserved polysaccharide) for ATP generation under anaerobiosis (wax ester fermentation) were promptly degraded immediately after the cells were replenished with sufficient O₂. A large part (about 70%) of the decomposed wax esters were converted back to paramylon.
• 2.2. When cells were fed with [1–14C]acetate or [U-¹⁴C]acetate immediately after transfer from anaerobic to aerobic conditions, radioactivity incorporated into paramylon in the cells fed with [U-¹⁴C]acetate was about 1.5-times as high as that with [1-¹⁴C]acetate, proposing that glyoxylate cycle participates in the conversion from wax esters to paramylon.
• 3.3. Paramylon synthesis from [1-¹⁴C]acetate was considerably activated by anaerobic preincubation of cells for several hours.
• 4.4. Isocitrate lyase and malate synthase occurred in cells cultured in Koren-Hutner medium, but the activities were obviously lower than those in cells grown on ethanol. These enzymes were not induced by the anaerobic preincubation.

     

Glucose metabolism in a kangaroo (Macropus robustus erubescens) and a similar size eutherian herbivore,the feral goat

• 1.1. Glucose pool size, space, entry rate, and turnover time were estimated from the specific radioactivity vs time curves of [³H] and [¹⁴C]glucose administered as a single injection in the euro (Macropus robustus erubescens) and the sympatric feral goat (Capra hircus).
• 2.2. Digestible energy intake was greater (P < 0.05 ± SE) in the goat than in the euro (798 ± 64 vs 624 ± 31kJ/kg^0.75 × day).
• 3.3. However, there were no significant differences between the two species in parameters of glucose metabolism.
• 4.4. The use of an implantable osmotic infusion pump to deliver isotopic glucose showed promise as a means of avoiding the stress involved with the single injection technique.

     

Neutral amino acid transport in an androgen-dependent epithelium

• 1.1. Transport of neutral amino acids by the isolated seminal vesicle epithelium of normal and gonadectomized guinea pigs has been investigated by measurement of the uptake of 2-amino[1-¹⁴C]-isobutyric acid and 2-methylamino[1-¹⁴C]isobutyric acid.
• 2.2. The V_max for Na-dependent and -independent transport of both amino acids was reduced by gonadectomy but the general transport characteristics appeared to be unchanged by this treatment.
• 3.3. The most likely explanation of the decreased transport is the loss of transporter molecules associated with the tissue regression that follows rapidly on gonadectomy.

     

Absorption of glucose,glycine and palmitic acid by isolated midgut and hindgut from crickets

• 1.1. In vitro experiments indicated that midgut and hindgut anterior to the Malpighian tubules are important in absorption and processing of products of digestion in crickets.
• 2.2. Isolated hindguts from crickets (Gryllus assimilis, G. rubens and Scapteriscus acletus) absorbed and released into the incubation medium 20–30% of a load of [¹⁴C]glucose and 29–31% of a load of[¹⁴C]glycine.
• 3.3. Isolated midguts from the same crickets absorbed and released into the incubation medium 30–50% of the glucose and 43–52% of the glycine load.
• 4.4. Radiolabelled palmitate was absorbed into epithelial cells of isolated mid- and hindguts, but little was transported and released into the incubation medium.

     

Metabolism of benzo[a]pyrene and persistence of DNA adducts in the brown bullhead (Ictalurus nebulosus)

• 1.1. The in vitro metabolism of [³H]benzo[a]pyrene (BP) and [¹⁴C]benzo[a]pyrene-7,8-dihydrodiol (BP-7,8-diol) by liver of brown bullhead (Ictalurus nebulosus) was characterized, as was the formation and persistence of BP-DNA adducts in vivo.
• 2.2. Compared to rat liver microsomes, bullhead liver microsomes produced relatively larger amounts of BP-7,8-diol (predominantly the [−] enantiomer) and smaller amounts of BP-4,5-diol.
• 3.3. BP phase I metabolites were efficiently converted by freshly isolated bullhead hepatocytes to conjugates, predominantly glucuronides.
• 4.4. BP-7,8-diol was metabolized by hepatocytes 4-fold more rapidly than was BP and was converted to approximately equal amounts of glucuronides, glutathione conjugates and sulfates.
• 5.5. BP-DNA adducts formed in bullhead liver with a lag time of several days and maximum adduct formation at 25–30 days. The major adduct was anti-BPDE-deoxyguanosine.

     

Gluconeogenesis in hepatocytes determined with [2-13C] acetate and quantitative 13C NMR spectroscopy

• 1.1. In the present study the major metabolic pathways of glucose metabolism were determined in isolated liver cells using [2-¹³C]acetate and ¹³C magnetic resonance spectroscopy.
• 2.2. The relative reaction rates of glucose synthesis to the TCA cycle were determined from the ¹³C distribution in glucose where the overall ¹³C enrichment of glucose was 6.41 ± 1.94% (mean ± SD; n = 6) and the mean ¹³C enrichment of C1, C2, C5, C6 to C3, C4 was 2.63 ± 0.30.
• 3.3. Since the distribution of tracer in glucose is a function of the relative entry rates of pyruvate to acetyl-CoA into the oxaloacetate pool this was calculated to be 0.32 ± 0.15 and the factor for carbon exchange (1/P) between the gluconeogenic pathway and the TCA cycle was calculated to be 1.03 ± 0.20.
• 4.4. With this carbon exchange factor and the approximated ¹³C enrichment of acetyl-CoA the intramitochondrial ¹³C enrichment of phosphoenolpyruvate was calculated and the “true” rate of hepatic gluconeogenesis from phosphoenolpyruvate estimated.
• 5.5. Since acetate was metabolized solely in liver cells the ¹³C enrichment of acetyl-CoA could be approximated from that of 3-hydroxybutyrate.
• 6.6. The carbon 13 enrichment of 3-hydroxybutyrate and phosphoenolpyruvate was 5.89 ± 0.90% and 5.96 ± 1.67%, respectively.
• 7.7. The per cent gluconeogenesis from phosphoenolpyruvate calculated as the ratio of the ¹³C enrichment of glucose to that of 3-hydroxybutyrate times 1/P was 107 ± 8%.
• 8.8. In this study the validity of assessing isotopic exchange at oxaloacetate as suggested by Katz [Katz J. (1985) Am. J. Physiol.248, R391–R399] when interpretation of the data are not obscured by pseudoketogenesis.
• 9.9. Magnetic resonance spectroscopy provides direct information about intramolecular tracer distribution by which flux rates in major metabolic pathways are derived.

     

Fate of ingested leucine and glucose in the sea star,Asterias rubens,during its annual reproductive cycle

• 1.1. The distribution of radiolabel from L-leucine [¹⁴C-UL] and D-glucose [¹⁴C-UL] was measured in the sea star Asterias rubens at 1, 6 and 24 hr after oral administration.
• 2.2. Incorporation of the label from both compounds was observed in pyloric caeca, coelomocytes and ovaries even after an incubation time of 1 hr.
• 3.3. Highest incorporation from both precursors was found in proteins, while substantial radioactivity was present in the amino acids, organic acids and neutral components. Lipids were hardly labelled from leucine and only slightly from glucose.
• 4.4. Radioactivity in proteins and lipids increased with increasing incubation time. No significant differences were found in the distribution patterns of radiolabel during the reproductive cycle.
• 5.5. The data obtained are discussed in terms of current knowledge on the translocation of nutrients in echinoderms.

     

Intramitochondrial reductive carboxylation of 2-oxoglutarate in adipose tissue and its contribution to fatty acid synthesis

• 1.1. The reductive carboxylation of 2-oxoglutarate was found to proceed in mitochondria of rat epididymal fat pads and rabbit perirenal adipose tissue at a rate similar to that in liver mitochondria.
• 2.2. In rat fat pads the incorporation of ¹⁴C from [5-¹⁴C]2-oxoglutarate into fatty acids via the carboxylation was suppressed by butylmalonate by 30%.
• 3.3. 2-Oxoglutarate and glutamate stimulated the incorporation into fatty acids of ¹⁴C from [2-¹⁴C]acetate in rat fat pads with the simultaneous reduction of tissue NADP. These effects persisted after inhibition of succinate dehydrogenase by malonate.
• 4.4. It is concluded that in adipose tissue 2-oxoglutarate carboxylation proceeds in both the cytoplasm and mitochondria. Therefore, it can supply carbon atoms as well as NADPH for fatty acid synthesis.

     

Light-induced transient increase of the activity of topoisomerase I in plasmodia of Physarum polycephalum

• 1.1. Activity of topoisomerase I and incorporation of [³H]uridine and [¹⁴C]thymidine were monitored during light-induced sporulation of the slime mold Physarum polycephalun.
• 2.2. A 4-fold transient increase of topoisomerase I activity but not of [³H]uridine or [¹⁴C]thymidine incorporation was observed after 42 hr of illumination with 6 hr impulses.
• 3.3. The activity of topoisomerase I did not increase in the absence of light impulses. However, ca 5-fold increase of the activity was observed in dark when 100 μ M dibutyryl-cAMP was administered 12 hr before harvesting of plasmodia.
• 4.4. Fluorodeoxyuridine and cycloheximide administered 36 hr after starting of the illumination cancelled the increase of the activity of topoisomerase I.
• 5.5. After 7 days of the illumination, when fruiting bodies appeared, the activity of topoisomerase I dropped to about 15% of the initial value.

     

Biosynthesis of lipid-linked oligosaccharides in embryonic liver. Glucosylation of mannose containing dolichyl diphosphate oligosaccharide

• 1.1. A maximum rate of dolichyl phosphate [¹⁴C]glucose synthesis from 55-day embryos was achieved at 16nM concentration of exogenous dolichyl phosphate and exceeded about 3 times that without addition of dolichyl phosphate.
• 2.2. The highest values of [¹⁴C]glucose incorporation from UDP-[¹⁴C]glucose into dolichyl phosphate [¹⁴C]glucose, dolichyl diphosphate [¹⁴C]Glc-oligosaccharides and proteins were reached at 5 min time point of incubation of liver microsomes both from embryos and sows.
• 3.3. The radioactive incorporation into proteins was about 7-fold higher in liver microsomes from sows compared to that from embryos, probably due to the greater content of acceptor proteins in microsomes from sows.
• 4.4. The enzymatic transfer of Glc₃-oligosaccharide from a lipid carrier to endogenous protein acceptor in microsomes from pig embryonic and adult livers was considerably faster than the removal of glucose residues during the initial stages of processing of protein-bound oligosaccharides.
• 5.5. One labelled compound was discovered in the Chcl₃-Ch₃Oh-H₂O (1:1:0.3, by vol) extract after incubation of liver microsomes from embryos and sows with UDP-[¹⁴C]glucose. On the basis of its mobility on the chromatogram it appears to be GlcNAc₂Man₉Glc₃.

     

Metabolic utilization of leucine in a fat and a lean line of chicken

• 1.1. In vivo incorporation into body lipids and breast muscle proteins from l-[U-¹⁴C]leucine was studied in genetically lean or fat male chickens, fed or starved, 1 or 24 hr after intraperitoneal injection.
• 2.2. Lipogensis and portein synthesis from labelled leucine were significantly higher in fat chickens than in lean birds, particularly in those in the fed state.
• 3.3. Radioactivity in the free amino acid pool was greater in fat birds irrespective of the nutritional state.
• 4.4. However, utilization of injected l-[U-¹⁴C]leucine for lipogenesis was no more than 2%.

     

Identification of a glycoprotein complex containing a glycogen synthase isozyme in Ascaris Suum obliquely-striated muscle

• 1.1. A glycogen/protein complex which contains the major portion of glycogen synthase activity in Ascaris suum muscle has been purified.
• 2.2. The complex contains two proteins which can be dissociated from a glycoprotein component.
• 3.3. The glycoprotein contains glycogen-like domains and is resistant to trypsin digestion.
• 4.4. The glycogen synthase activity in the purified complex catalyzes glycogen synthesis in the absence of exogenous glycogen, but demonstrates an absolute glucose 6-phosphate requirement for activity.
• 5.5. The data support the hypothesis that this isozyme of glycogen synthase is significantly different from the cyclic AMP-regulated enzyme.

     

Carbohydrate metabolism in several tissues of rainbow trout,Oncorhynchus mykiss,is modified during ovarian recrudescence

• 1.1. Several pathways of carbohydrate metabolism were evaluated in three different tissues—liver, gonad and kidney—of a hatchery-reared population of rainbow trout (Oncorhynchus mykiss) which characterised two different stages of their gonadal maturation, i.e. previtellogenesis and established exogenous vitellogenesis.
• 2.2. A fall in liver glycogen levels was observed during exogenous vitellogenesis. A decrease in activity of the enzymes involved in glycolysis and in the pentose phosphate shunt was also observed, suggesting that at the end of exogenous vitellogenesis the necessity of energy and reducing power has decreased compared to the situation at the onset of this period.
• 3.3. The main changes observed in gonad during vitellogenesis were the decreased activity of glycolysis and the pentose phosphate shunt as well as increased glycogen levels. The stored glycogen should be used later in association with the embryo development.
• 4.4. No major changes were observed in kidney metabolism throughout the vitellogenic process.
• 5.5. Exogenous vitellogenesis in rainbow trout is mainly associated with increased glycogen levels in the gonad and decreased metabolic activity in the liver.

     

Effect of inorganic phosphate on synthesis of 5-phosphoribosyl-1-pyrophosphate in cultured plant cells

• 1.1. Inorganic phosphate (Pi) was absorbed rapidly by suspension-cultured cells of Catharanthus roseus which had previously been cultured in Pi-free Murashige Skoog medium.
• 2.2. The intracellular levels of ATP, ADP and 5-phosphoribosyl-l-pyrophosphate (PRPP) increased markedly during the 24 hr which followed the addition of Pi (1.25mM).
• 3.3. Availability of PRPP in vivo, estimated by the measurement of nucleotide synthesis from [8-¹⁴C]adenine, was also increased by addition of Pi.
• 4.4. Only a 20% increase in the maximum catalytic activity of PRPP synthetase was observed in extracts of cells, prepared 24 hr after addition of Pi.
• 5.5. In contrast to results for mammalian PRPP synthetase, the activity of PRPP synthetase, partially purified from Catharanthus roseus, was inhibited by concentration of Pi greater than 5mM.
• 6.6. The mechanisms involved in the increased availability of PRPP and the synthesis of adenine nucleotides in the plant cells cultured in Pi-containing medium are discussed.

     

In vitro absorption of [14C]leucine during inflammation and the effect of antiinflammatory drugs in the jejunum of rats

• 1.1. Inflammation was induced in the hindlegs of rats by formalin injection and the in vitro absorption of [¹⁴C]leucine was studied.
• 2.2. Treatment of rats with formalin caused a reduction in the in vitro absorption of leucine from the mucosa of jejunum.
• 3.3. Oral administration of oxyphenbutazone or a herbal anti-inflammatory drug (Withania somnifera) prior to formalin injection resulted in no alteration in the jejunal absorption of [¹⁴C]leucine.