Stimulation by autologous serum preheated at 66 °C of the incorporation of [3H]uridine by cultured lymphocytes: comparison with stimulation by concanavalin A

1977 ◽  
Vol 55 (3) ◽  
pp. 215-222 ◽  
Author(s):  
C. M. David ◽  
D. R. Forsdyke
Keyword(s):  
Concanavalin A ◽  
Maximum Velocity ◽  
Autologous Serum ◽  
Rabbit Serum ◽  
Con A ◽  
Rate Limiting Step ◽  
Inhibitory Molecule ◽  
Lymph Node Cells ◽  
Stimulatory Factor ◽  
Rate Limiting

Rabbit serum, preheated at 66 °C for 30 min, produced a stimulation of the incorporation of [3H]uridine by cultured autologous lymph-node cells similar to that caused by concanavalin A (Con-A). However, whereas the percentage stimulation by Con-A increased with time, that by serum preheated at 66 °C (66 °C-serum) reached a peak after 3–4 h and then declined. The decline was greater at higher cell concentrations. Isotope-dilution studies showed that stimulation at 3 h by 66 °C-serum or by Con-A reflected an increase in the maximum velocity of the rate-limiting step for incorporation of [3H]uridine and not a decrease in the pool of uridine and (or) uridine competitors. Experiments in which serum concentration and the relative proportions of serum preheated at 66 °C and serum preheated at 37 °C were varied, suggested that preheating serum at 66 °C removes an inhibitory factor and exposes a stimulatory factor. The stimulatory activity of 66 °C-serum was not dialysable. The results are compatible with a model which requires that lectins activate cultured lymphocytes by influencing the distribution of an inhibitory molecule (perhaps α2-macroglobulin) between the cell surface and the culture medium.

scholarly journals The steady state kinetics of the NADH-dependent nitrite reductase from Escherichia coli K12. The reduction of single-electron acceptors

1982 ◽  
Vol 203 (2) ◽  
pp. 505-510 ◽  
Author(s):  
R H Jackson ◽  
J A Cole ◽  
A Cornish-Bowden
Keyword(s):  
Escherichia Coli ◽  
Cytochrome C ◽  
Nitrite Reductase ◽  
Maximum Velocity ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Steady State Kinetics ◽  
Cytochrome C Reduction ◽  
Pattern Of Variation ◽  
Rate Limiting

The kinetic characteristics of the diaphorase activities associated with the NADH-dependent nitrite reductase (EC 1.6.6.4) from Escherichia coli have been determined. The values of the apparent maximum velocity are similar for the reduction of Fe(CN)6(3)-and mammalian cytochrome c by NADH. These reactions may therefore have the same rate-limiting step. NAD+ activates NADH-dependent reduction of cytochrome c, and the apparent maximum velocity for this substrate increases more sharply with the concentration of NAD+ than for hydroxylamine. The simplest explanation is that NAD+ activation of hydroxylamine reduction derives solely from activation of steps involved in the reduction of cytochrome c, a flavin-mediated reaction, but these steps are only partly rate-limiting for the reduction of hydroxylamine. At 0.5 mM-NAD+, the apparent maximum velocity was 2.3 times higher for 0.1 mM-cytochrome c as substrate than for 100 mM-hydroxylamine, suggesting that the rate-limiting step during hydroxylamine reduction is a step that is not involved in cytochrome c reduction. A scheme is proposed that can account for the pattern of variation with [NAD+] of the Michaelis-Menten parameters for hydroxylamine and for NADH with hydroxylamine or cytochrome c as oxidized substrate.

scholarly journals The capacity of mitogen-responsive T cells to home to their tissue of origin, analyzed by means of chromosome markers

1976 ◽  
Vol 143 (3) ◽  
pp. 660-671 ◽  
Author(s):  
MJ Doenhoff ◽  
AJS Davies
Keyword(s):  
T Cells ◽  
Lymph Node ◽  
Concanavalin A ◽  
Spleen Cells ◽  
Con A ◽  
Syngeneic Mouse ◽  
Lymph Node Cells ◽  
Mitogen Responsiveness ◽  
Tissue Of Origin ◽  
Syngeneic Recipient

Lance and Taub (1) showed that when radioactively labeled lymphocytes were injected into a syngeneic mouse and the lymph node cells of this animal transferred to a second syngeneic recipient, the proportion of radioactivity found in the lymph node relative to the amount present in the spleen of the secondary recipient had increased markedly. The interpretation of this result was that some lymphocytes have the capacity to home to their organ of origin. The purpose of the experiments described here was to test the homing copacity of T cells by a method that did not involve radioactive labeling. It has been shown elsewhere that some or all mouse T cells are stimulated to divide in culture by the mitogens phytohemagglutinin (PHA) and concanavalin A (Con A) (2). We therefore elected to inject karyotypically distinct lymphocytes into syngeneic recipients and to follow their subsequent distribution by culture of lymph node and spleen cells of the recipient with PHA or Con A. In this manner the homing capacities of spleen and lymph node T cells could be determined, and furthermore, the effects of labeling with chromium-51 ((51)Cr) could be assayed with respect to the persistence of mitogen responsiveness in the injected cells.

The threshold growth response ofLactobacillus caseito 5-methyl-tetrahydrofolic acid: implications for folate assays

1985 ◽  
Vol 53 (3) ◽  
pp. 569-573 ◽  
Author(s):  
A. J. A. Wright ◽  
D. R. Phillips
Keyword(s):  
Folic Acid ◽  
Growth Response ◽  
Current Knowledge ◽  
Basal Medium ◽  
Maximum Velocity ◽  
Rate Limiting Step ◽  
Absolute Growth ◽  
Tetrahydrofolic Acid ◽  
Rate Plot ◽  
Rate Limiting

1. The comparative and absolute growth response of Lactobacillus casei was measured nephelometrically for time periods of 17–23 h in the microbiological assay of folic acid and 5-methyl-tetrahydrofolic acid at concentrations of 0–8 ng/10 ml basal medium at pH 6.8.2. At concentrations of 0–1 ng/10 ml the comparative growth response to 5-methyl-tetrahydrofolic acid was markedly depressed whereas growth was the same at 2 ng/10 ml and above. Comparative growth was unaffected by the length of assay incubation, depressed growth being due to differences in log-phase growth rates with the rate-plot for 5-methyl-tetrahydrofolic acid being sigmoidal and for folk acid being a rectangular hyperbola with linearity only in the 0–1 ng/10 ml range. The reciprocal rate-plot for folic acid was linear whereas that for 5-methyl-tetrahydrofolic acid was coincidental only in part, giving rise to the same estimate of maximum velocity and substrate concentration for half-maximum velocity, with the exhibition of a strong threshold at low concentration.3. A previous observation (Phillips & Wright, 1982) that the L. casei growth response to 5-methyl-tetrahydrofolic acid may be significantly less than that to folic acid is confirmed as is the long-established view that the response to both folates may be equal. In the light of current knowledge regarding folate-binding, transport and metabolism by L. casei, it is argued that the intracellular oxidation of 5-methyl-tetrahydrofolic acid to 5, 10-methylene-tetrahydrofolic acid is a rate-limiting step at low substrate concentrations, subsequently giving rise to a threshold growth response peculiar to 5-methyl-tetrahydrofolic acid. Since the rate of L. cusei growth with folk acid is not linearabove 1 ng/10 ml, it is recommended that microbiological folate assays be conducted only in the 0–1 ng/10 ml range and at a pH that elicits the same growth response from L. casei to 5-methyl-tetrahydrofolic acid as to folic acid and other folate monoglutamates.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Concanavalin A-induced Aggregation of Human Blood Platelets

1975 ◽  
Vol 33 (02) ◽  
pp. 354-360 ◽  
Author(s):  
Heinrich Patscheke ◽  
Reinhard Brossmer
Keyword(s):  
Concanavalin A ◽  
Binding Capacity ◽  
Specific Binding ◽  
Blood Platelets ◽  
Residual Effect ◽  
Independent Effect ◽  
Con A ◽  
Experimental Conditions ◽  
Main Effect ◽  
Induced Aggregation

SummaryConcanavalin A (CON A) causes platelets to aggregate. A Ca++-independent effect of CON A could be separated from a main effect which depends on Ca++. The main effect probably is a consequence of the CON A-induced platelet release reaction and therefore is platelet-specific. The weak residual effect observed in the presence of Na2EDTA may be due to a similar mechanism as has been demonstrated for CON A-induced aggregations of several other normal and malignant transformed animal cells.Na2EDTA did not inhibit the carbohydrate-specific binding capacity of CON A. Therefore, Na2EDTA appears not to demineralize the CON A molecules under these experimental conditions.α-methyl-D-glucoside inhibits the Ca++-independent as well as the Ca++-dependent effect of CON A.Pretreatment by neuraminidase stimulated the platelet aggregation induced by CON A. It is possible that removal of terminal sialic acid residues makes additional receptors accessible for the binding of CON A.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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