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T T Ngo

Publications and source records attributed to T T Ngo.

At least 19 recordsLinked to original sources
PubMed1991

Immunoassay.

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Animals↗
PubMed1979

Kinetics of acetylcholinesterase immobilized on polyethylene tubing.

Acetylcholinesterase was covalently attached to the inner surface of polyethylene tubing. Initial oxidation generated surface carboxylic groups which, on reaction with thionyl chloride, produced acid chloride groups; these were caused to react with excess ethylenediamine. The amino groups on the surface were linked to glutaraldehyde, and acetylcholinesterase was then attached to the surface. Various kinetic tests showed the catalysis of the hydrolysis of acetylthiocholine iodide to be diffusion controlled. The apparent Michaelis constants were strongly dependent on flow rate and were much larger than the value for the free enzyme. Rate measurements over the temperature range 6-42 degrees C showed changes in activation energies consistent with diffusion control.

Acetylcholinesterase↗
PubMed1979

Activation by adenosine-5'-triphosphate of glutamic decarboxylase from a subcellular fraction of mouse brain.

Glutamate decarboxylase from a mouse brain P2 fraction undergoes a twofold activation in the presence of 0.5 mM ATP. No such stimulation by ATP occurs if the enzyme is assayed in the presence of excess pyridoxal phosphate as cofactor. The ATP-induced stimulation is almost completely eliminated if the enzyme is dialysed before its assay. [lambda-32P]ATP present during the enzyme measurement is converted to [32P]pyridoxal phosphate. These results demonstrate that the activation produced by ATP is the result of the generation of cofactor during the course of the assay. This phenomenon may be a reflection of a control mechanism of glutamate decarboxylase activity.

Adenosine Triphosphate↗
PubMed1978

Functional role of arginine residues in glutamic acid decarboxylase from brain and bacteria.

The arginine-specific reagent phenylglyoxal rapidly inactives glutamic decarboxylase from both mouse brain and E. coli when preincubated with the enzyme at concentrations of 3 mM to 40 mM. The rate of inactivation follows pseudo-first-order kinetics and is dependent upon the concentration of phenylglyoxal. These and other data presented support the idea that arginine residues play a key role in the mechanism of action of glutamic decarboxylase.

Animals↗
PubMed1978

Temperature and pH effects with immobilized electric eel acetylcholinesterase.

Kinetic studies were made with 2 forms of immobilized acetylcholinesterase: enzyme trapped in polyacrylamide gel which was cut into slices; and enzyme attached to the inner surface of nylon tubing. Rates were measured at substrate concentrations which were low and high with reference to the Michaelis constant, and over the temperature range 16-40 degrees C. Low activation energies (1.7-2.7 kcal mol-1) were obtained at low substrate concentrations, indicating diffusion control. At high substrate concentrations the Arrhenius plots were non-linear and the activation energies substantially higher, and there is less diffusion control. With enzyme-polyacrylamide slices, there was a continuous increase in rate with increasing pH, in contrast to the bell-shaped behavior with free enzyme. A theoretical treatment suggests that this is due to the lowering of local pH as a result of the acid released in the hydrolysis.

Acetylcholinesterase↗
PubMed1978

Regulation of brain pyruvate dehydrogenase multienzyme complex.

A number of excellent and comprehensive reviews on various aspects of pyruvate dehydrogenase multienzyme complex have been written recently. The purpose of the present review is to summarize briefly the reaction mechanism and the regulation of this enzyme. Emphasis is put on the most recent literature not covered by previous reviews. Particular attention is also paid to the regulation of brain pyruvate dehydrogenase multienzyme complex, since a number of patients with neuromuscular diseases, such as Friedreich's ataxia, show a decreased rate of pyruvate oxidation.

Animals↗
PubMed1978

Lipoamide dehydrogenase regulation in rat brain.

The Pyruvate dehydrogenase multienzyme complex (PDHC) purified from rat brain is phosphorylated in the presence of low concentrations of ATP and MgCl2. The phosphorylated PDHC is incapable of catalyzing the oxidative decarboxylation of pyruvate. In the presence of high concentrations (10 mM) of MgCl2, the phosphorylated (inactive) PDHC is converted back to the dephospho-form of PDHC which is catalytically active. The dihydrolipoyl dehydrogenase (LAD) component, E3, of PDHC is inactivated by pyridoxal phosphate (PLP) and the PLP-inactivated LAD can be reactivated by an amino acid, taurine. These results indicate the reversible formation of Schiff base between PLP and LAD. They also provide clear evidence for the involvement of LAD (E3) in the previously reported inactivation of PDHC by PLP.

Adenosine Triphosphate↗