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T Liang

Publications and source records attributed to T Liang.

At least 73 records · Page 4Linked to original sources
PubMed1979

Substance P stimulation of amylase release by isolated parotid cells and inhibition of substance P induction of salivation by vasoactive peptides.

Substance P stimulation of salivation in rats has been studied as has its in vitro enhancement of amylase release by isolated parotid cells. The extent of the stimulation on amylase release by isolated parotid cells was dependent upon the concentration of substance P, with the minimum effective concentration being 1 nM. The substance P effect was detectable within 1 min after incubation and lasted for at least 50 min. Substance P stimulation was demonstrable at 25--37 degrees C but not at 0 degrees C. Adrenocorticotropic hormone (ACTH), thyrotropin-releasing hormone (TRH), vasopressin and neurotensin had no effect on amylase release. These results suggest that substance P may act directly on the parotid cells. Examination of the salivary-stimulating activity of fragments of substance P showed that the C-terminal octapeptide and (pyroglutamyl)hexapeptide were active, although less potent than substance P, whereas its free acid, C-terminal tetra- and tri-peptides were inactive. Vasopressin, angiotensin II and neurotensin could inhibit substance P induced salivation, whereas TRH, ACTH and somatostatin had no effect. Amylase activity per unit volume of saliva was not changed by the injection of vasopressin, angiotensin II or neurotensin. These vasoactive peptides did not affect substance P stimulation of amylase release by isolated parotid cells. The results indicate that vasopressin, angiotensin II and neurotensin inhibit the action of substance P on salivation at sites other than the parotid cells.

Acetylcholine↗
PubMed1978

Selective polyamine-binding proteins. Spermine binding by an androgen-sensitive phosphoprotein.

Rat ventral prostate contains an acidic protein which can bind spermine selectively. The relative binding affinities of various aliphatic amines for the protein are, in decreasing order, spermine greater than thermine greater than greater than putrecine greater than 1,10-diaminodecane, cadaverine and 1,12-diaminododecane. The binding protein has an isoelectric point at pH 4.3 and a sedimentation coefficient of 3 S. Its molecular weight is approx. 30 000. Histones and nuclear chromatin preparations of the prostate can interact with the binding protein. The spermine-binding activity of the purified prostate protein can be inactivated by treatment with intestinal alkaline phosphatases. The phosphatase treated preparation can then be reactivated by beef heart protein kinase in the presence of cyclic AMP and ATP. The spermine-binding activity of the prostate cytosol protein fraction decreases after castration, but increases very rapidly after the castrated rats are injected with 5alpha-dihydrotestosterone. This finding raises the possibility that, in the postate, certain androgen actions may be dependent on the androgen-induced increase in the acidic protein binding of polyamines and their translocation to a functional cellular site such as nuclear chromatin. In the prostate cytosol, spermine also binds to 4-S tRNAs and to a unique RNA which has a sedimentation coefficient of 1.5 S.

Androgens↗
PubMed1976

Inhibition of P-enolpyruvate carboxykinase and of glyconeogenesis in Tetrahymena by 3-mercaptopicolinic acid.

Tetrahymena grown overnight in deep cultures were incubated for 1 hr with [1-14C]labeled substrates in the presence or absence of 3-mercaptopicolinic acid (3MPA). 3-MPA inhibited appearance of label in glycogen from bicarbonate, acetate, pentanoate, octanoate, and succinate, but not from glycerol or glucose. In vitro assays of phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase activity showed that both enzymes were about equally distributed between the particulate and cytosol fractions. 3-MPA inhibited phosphoenolpyruvate carboxykinase from both the cytoplasmic and particulate fractions, but had no effect on phosphoenolpyruvate carboxylase from either location. These results suggest that the in vivo effects of this drug are due to inhibition of glyconeogenesis at this site.

Acetates↗
PubMed1976

Effect of 4-pentenoic acid on intermediate metabolism of Tetrahymena.

The growth of Tetrahymena pyriformis strain HSM was strongly inhibited by 4-pentenoic acid. Supplementing the medium acetate reversed the growth inhibition, but pyruvate was ineffective. Glycogen content was much lower in cells grown with 4-pentenoic acid than in controls; this effect was not reversed by acetate or by pyruvate. There was little effect of 4-penteonic acid on the in incorporation of label from [1-14C]acetate, [2-14C]glycerol, [1-14C]ribose, [U-14C]fructose, or [1-14C]glucose into CO2 but incorporation of label into glycogen was inhibited, the strongest inhibition being on acetate and the weakest approximately 20%) on ribose, fructose, and glucose. A 3-compartment model for quantitation of labeled acetyl CoA fluxes was shown to be applicable to Tetrahymena grown in the presence of 4-pentenoic acid, and experiments were performed to establish the flux of [1-14C]acetyl CoA into glycogen, lipids, CO2, glutamate, and alanine. It was evident from the results of these experiments that 4-pentenoic acid did not appreciably inhibit beta-oxidation or lipogenesis, but markedly decreased the glyconeogenic flux of labeled acetyl-CoA from the peroxismal and outer mitochondrial compartments.

Acetates↗
PubMed1975

A quantitative analysis of metabolite fluxes along some of the pathways of intermediary metabolism in Tetrahymena pyriformis.

A detailed model of intermediary metabolism has been constructed which is consistent with all known information on the compartmental structure of metabolism in Tetrahymena, on the enzyme complement of this cell, and on the localization of the enzymes. The model allows computation of the specific activity of every carbon atom of all metabolites and thus of the flux of carbon along the major pathways of metabolism under steady state conditions. To test the model, data were required from cells grown under standard conditions and then suspended in a dilute salt solution and incubated for 1 hour in a mixture of acetate, pyruvate, hexanoate, bicarbonate, and glutamate labeled in a total of 10 positions, but with only one substrate labeled in any given flask. Twenty-seven measurements of label incorporation into CO2, lipids, glycogen, glutamate, and alanine were made, plus measurements of label distribution into fatty acid and glycerol moieties for 4 of the substrates and of oxygen consumption and of glycogenolysis, yielding 33 independent measurements. These, plus about 18 "limit" measurements which also constrain any possible solutions, were in sufficient excess of the 23 independent parameters to permit a stringent assessment of the model. Equations derived directly from the structure of the model and from the known stereochemistry of the reactions were programmed on a PDP-15 computer and values of the Qo2 and of label expected to be incorporated into the various products actually measured were computed for any given set of flux rates. A set of flux rates was found which yielded an excellent fit to the observed data. The ability to achieve a fit to the data for an overdetermined system constitutes strong support for this structural model of intermediary metabolism and the computed flux rates therefore provide a quantitative description of metabolite flow in the intact cell. Despite the redundancy of measurements relative to parameters to be determined, it was not possible to define a unique set of values for the flux through phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase, although the relationship between these fluxes is specified by the model. The analysis allows estimation of the recycling of phosphoenopyruvate through pyruvate kinase under conditions of net glyconeogenesis and an apparently futile exchange of acetyl-CoA between the inner and outer mitochondrial compartments. Carbon flow through the glyoxylate bypass under these conditions is about one-third of that through the Krebs cycle. The analysis also shows a net transport of malate from the peroxisomes to the mitochondria, consistent with the anaplerotic role of the peroxisomal glyoxylate bypass in Tetrahymena.

Acetates↗
PubMed1975

Effect of oxygen on the regulation of intermediate metabolism in Tetrahymena.

Tetrahymena grown in poorly aerated cultures have a greater capacity to utilize oxygen than cells grown in relatively well aerated cultures. Paradoxically, the oxidation of (1-14C)-glucose was inhibited, while oxidation of (2-14C)pyruvate and (2-14C)glyoxylate was enhanced in cells grown under relatively anaerobic conditions. Total glycogen content measured after 17 hours of growth was increased 30 to 60% in cells grown partially anaerobically. In 1-hour incubations at the end of this time, the capacity to incorporate label into glycogen from (1-14C)pyruvate and (2-14C)glyoxylate was increased several fold. The ratio of adenosine di- and triphosphates was nearly identical in the cells grown under different conditions of oxygenation, indicating that this ratio may not play a major role in regulating these changes. After 17 hours of growth in cultures of different depths, cells were also incubated with a mixture of acetate, pyruvate, and octanoate, with one substrate labeled at a time in such a way that (1-14C)-acetyl-CoA is generated at the initial step in the metabolism of each. These results were interpreted in terms of a previously developed three-compartment model of acetyl-CoA metabolism. Glyconeogenesis from peroxisomal and mitochondrial precursors was increased in cells grown in low oxygen tension, with the greater contribution coming from the peroxisomes. Oxidation of acetate and pyruvate was increased under these conditions, but appearance of (1-14C)-acetate label in glutamate was decreased. Lipogenesis from labeled peroxisomal precursors was also increased in cells grown under relatively low oxygen tension. After a shift down in O2 tension there is a rapid rise in glyconeogenesis from the peroxisomes which levels off after about 4 hours, whereas the rate of oxidation in the Krebs cycle increases steadily for at least 8 hours following the transition to relatively anaerobic conditions. In response to a shift up in O2 tension there is a decline in peroxisomal glyconeogenesis which continues for 8 hours, whereas the rate of oxidation in the Krebs cycle does not begin decreasing until about 4 hours after the increase in O2 tension. Thus the flux of (1-14C)acetyl-CoA changes according to a different temporal pattern in mitochondria as compared to peroxisomes, and in each compartment the sequence of changes in response to a shift up in O2 tension is not the mirror image of the sequence in response to a shift down.

Acetyl Coenzyme A↗
PubMed1975

A very rapid effect of androgen on initiation of protein synthesis in prostate.

The initiation of protein synthesis by ribosomal particles of rat ventral prostate was studied by measuring ribosomal binding of an initiator (35-S)methionyl-tRNAf. The binding activity is dependent on ribosomes, GTP, and a prostate cytosol protein fraction. The 40S but not the 60S ribosomal subunit particles are active. The cytosol activity decreases rapidly within one hour after the rat is castrated. This loss is prevented by an intraperitoneal injection of 17beta-hydroxy-5-alpha-androstan-3-one (5-alpha-dihydrotestosterone). The cytosol activity can be stimulated almost immediately (within 10 min) after an intravenous injection of low dose (15 mug per rat) of 5-alpha-dihydrotestosterone into the castrated rat.

Animals↗