Glucose, glutamine and ketone body utilisation by resting and concanavalin A activated rat splenic lymphocytes

The utilisation of glucose, glutamine, acetoacetate and D-3-hydroxybutyrate were investigated over 72 h of incubation of rat splenic lymphocytes, with and without concanavalin A. Lymphocytes consumed both ketone bodies; acetoacetate was consumed preferentially. The ketone bodies reduced glucose consumption by 30-50%, but had little effect on lactate production. Glutamine uptake was concentration dependent up to 4 mM, and consumption was increased in the presence of concanavalin. Glutamine stimulated glucose consumption and lactate production in both resting and activated cells. Complete oxidation contributed 65% of glucose-derived ATP, but less than 40% of glutamine-derived ATP. Glutamine metabolism makes only a minor contribution to lymphocyte ATP generation.     

The transport of glutamine into rat mesenteric lymphocytes

The transport of glutamine into isolated rat mesenteric lymphocytes was studied. This transport appears to be dependent upon the Na+ gradient. The Km for glutamine transport was about 1.0 mM. A large number of amino acids were shown to inhibit the rate of transport of both serine and glutamine into lymphocytes. The transport of glutamine was competitively inhibited by serine and that for serine was similarly inhibited by glutamine. In contrast, histidine and 2-(methylamino)isobutyrate inhibited the transport of both serine and glutamine noncompetitively. It is concluded that glutamine is transported into rat mesenteric lymphocytes by a process similar to System ASC described for other cells.     

De novo purine synthesis in human lymphocytes. Partial co-purification of the enzymes and some properties of the pathway

A partially purified enzyme extract from lectin-transformed human peripheral blood lymphocytes synthesized purine nucleotides de novo. Although the relatively lower specific activity of the pathway compared with that in the avian liver preparation previously described (Rowe, P. B., McCairns, E., Madsen, G., Sauer, D., and Elliott, H. (1978) J. Biol. Chem. 253, 7711-7721) limited the extent of purification, a number of properties were established: (i) Ammonia could be utilized as readily as glutamine for the synthesis of phosphoribosylamine but only glutamine provided N-3 of the purine ring; (ii) in the presence of either GTP or NAD, AMP or GMP were synthesized; (iii) purine synthesis was inhibited at the level of phosphoribosylamine synthesis by both AMP and GMP, irrespective of whether ammonia or glutamine was the N donor; (iv) while the synthesis of AMP and GMP from IMP was self-regulated, GTP also appeared to be an inhibitor of the synthesis of GMP from IMP; (v) amidophosphoribosyltransferase was isolated from both transformed and nontransformed cells in a low molecular weight form which was converted to a high molecular weight form in the presence of GMP; and (vi) no evidence was obtained for the existence of a classical multienzyme complex for purine synthesis.     

Intracellular distribution of tetracyclines in rat hepatocytes

Distribution of tetracyclines, such as oxytetracycline, morphocycline, tetracycline, doxicycline and methacycline in the liver cells of rats was studied. The ratio of the subcellular structures, i. e. nuclei, mitochondria and microsomes and the liquid phase containing the drugs in the dissolved state in the system studied was close to the natural ratio of the hepatocyte organoids and cytoplasm. Distribution of tetracyclines in the subcellular fractions was not uniform. The nuclei did not absorb the drugs. The role of microsomes in drug absorption was insignificant. The mitochondria bound the highest amounts of the drugs and defined the characteristics of their intracellular distribution. The amounts of the drugs in the active form remaining in the cytoplasm after their contact with organoids were low. At the same time there was observed a a definite activating effect of the cytoplasm components on the antibiotics contained in it.     

Intracellular distribution of enzymes associated with nitrogen assimilation in roots

The cellular distribution of enzymes involved in nitrogen assimilation: nitrate reductase (EC 1.6.6.2), nitrite reductase (EC 1.6.6.4), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), and glutamate dehydrogenase (EC 1.4.1.3) has been studied in the roots of five plants: maize (Zea mays L. hybrid W 64A x W 182E), rice (Oryza sativa L. cv. Delta), bean (Phaseolus vulgaris L. cv. Contender), pea (Pisum sativum L. cv. Demi-nain), and barley (Hordeum vulgare L.). Initially, cell organelles were separated from soluble proteins by differential centrifugation. Cell organelles were also subjected to sucrose density gradients. The results obtained by these two methods indicate that nitrite reductase and glutamate synthase are localized in plastids, nitrate reductase and glutamine synthetase are present in the cytosol, and glutamate dehydrogenase is a mitochondrial enzyme.     

Intracellular distribution of fumarase in rat skeletal muscle

The distribution of fumarase activity between the mitochondrial and cytoplasmic compartments of rat skeletal muscle was studied using the method of Fatania and Dalziel (Biochim. Biophys. Acta 631 (1980) 11–19), fractional extraction technique and a method based on the calculation of mitochondrial protein content in the tissue and on the determination of fumarase activity both in the tissue homogenate and in the isolated mitochondria. We found 10%, 5% and 0% of the total fumarase activity in the cytoplasm using these methods, respectively. The results suggest that no more than 10% of the total fumarase activity is present in the cytosolic fraction of rat skeletal muscle. The metabolic consequences of such distribution of fumarase in skeletal muscle are discussed.