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Biomedical subjects

L L Lee

Publications and source records attributed to L L Lee.

At least 37 records · Page 2Linked to original sources
PubMed1987

Thermal stability of proteins in the presence of poly(ethylene glycols).

Thermal unfolding of ribonuclease, lysozyme, chymotrypsinogen, and beta-lactoglobulin was studied in the absence or presence of poly(ethylene glycols). The unfolding curves were fitted to a two-state model by a nonlinear least-squares program to obtain values of delta H, delta S, and the melting temperature Tm. A decrease in thermal transition temperature was observed in the presence of poly(ethylene glycol) for all of the protein systems studied. The magnitude of such a decrease depends on the particular protein and the molecular size of poly(ethylene glycol) employed. A linear relation can be established between the magnitude of the decrease in transition temperature and the average hydrophobicity of these proteins; namely, the largest observable decrease is associated with the protein of the highest hydrophobicity. Further analysis of the thermal unfolding data reveals that poly(ethylene glycols) significantly effect the relation between delta H degrees of unfolding and temperature for all the proteins studied. For beta-lactoglobulin, a plot of delta H versus Tm indicates a change in slope from a negative to a positive value, thus implying a change in delta Cp in thermal unfolding caused by the presence of poly(ethylene glycols). Results from solvent-protein interaction studies indicate that at high temperature poly(ethylene glycol) 1000 preferentially interacts with the denatured state of protein but is excluded from the native state at low temperature. These observations are consistent with the fact that poly(ethylene glycols) are hydrophobic in nature and will interact favorably with the hydrophobic side chains exposed upon unfolding; thus, it leads to a lowering of thermal transition temperature.

Chymotrypsinogen↗
PubMed1987

Dissolution of gallstones using cholecystostomy tube in the pig.

Cholecystostomy catheters and human cholesterol gallstones were implanted surgically in the gallbladders of eight pigs. Through the catheters, mono-octanoin or sterile water (H2O) was infused from two to seven days. The mono-octanoin dissolved pure cholesterol gallstones smaller than 200 g. There was no stone dissolution with infusion of sterile water and only one stone larger than 250 g was dissolved with mono-octanoin. Side effects included moderate-to-severe inflammation and ulceration of the gallbladder with mono-octanoin instillation, which precludes its widespread use with the present treatment regimen. Infusion of water caused little gallbladder irritation.

Animals↗
PubMed1987

A panic attack in therapeutic recreation over being considered therapeutic.

Ancillary professions have been called upon to account for therapeutic benefits from their services or be eliminated from the health care system. A singular focus on therapy, however, would negate the unique contribution of therapeutic recreation within, while simultaneously restricting services to health care settings. It is proposed that panic over therapeutic recreation services meeting health care goals has hindered evaluation and solidification of the leisure-based philosophy presented in the NTRS Philosophical Position Statement (NTRS, 1982). It is argued that emphasizing the leisure orientation of the philosophical position statement can secure therapeutic recreation's position within, yet, not deny services to those outside of the health care system. An overview is presented on the adequacy of the position statement philosophy for therapeutic recreation. A potential danger of attempting to explain therapeutic recreation in terms of non-leisure based philosophies is also discussed.

Humans↗
PubMed1986

Dissolution of cholesterol gallstones: comparison of solvents.

Various gallstone solvents are compared to evaluate their efficacy. Cholesterol gallstones from 5 patients were weight matched and incubated in 5 different solutions at 37 degrees C. These solutions consisted of methyl-tertiary butyl ether (MTBE), 90% mono-octanoin (MO), absolute alcohol, normal saline, and water. Absolute alcohol and MTBE were found to induce faster stone dissolution than the mono-octanoin derivative. Concentrations of alcohol below 80%, normal saline, and water were not effective in dissolving stones. Newer agents such as MTBE may prove valuable in dissolution of stones in the human gallbladder or bile ducts.

Caprylates↗
PubMed1985

Equilibrium and rapid kinetic studies on nocodazole-tubulin interaction.

The interaction between nocodazole and calf brain tubulin in 10(-2) M sodium phosphate, 10(-4) M GTP, and 12% (v/v) dimethyl sulfoxide at pH 7.0 was studied. The number of binding sites for nocodazole was shown to be one per tubulin monomer of 50,000 as a result of equilibrium binding studies by gel filtration and spectroscopic techniques. The presence of microtubule-associated proteins did not significantly affect the binding of nocodazole to tubulin. The apparent equilibrium constant measured at 25 degrees C was (4 +/- 1) X 10(5) M-1. Temperature does not significantly affect the apparent equilibrium constant; hence, the binding of nocodazole to tubulin is apparently entropy driven. Stopped flow spectroscopy was employed to monitor the rate of nocodazole binding under pseudo first order conditions. The effects of temperature and nocodazole concentration were studied. The apparent rate constants were dependent on the concentration of nocodazole in a nonlinear manner. In conjunction with results from structural and thermodynamic studies the kinetic results were interpreted to suggest a mechanism of T + N in equilibrium with TN in equilibrium with T* N, where T and N are tubulin and nocodazole, respectively. T and T* represent two conformational states of tubulin. Furthermore, the kinetic data are consistent with the thermodynamic data only if a model of two parallel similar reactions were considered, one rapid and the other slow. The initial binding step for both the rapid and slow phases was characterized by identical binding constants; however, there was a significant difference in the rates of isomerization. Hence, nocodazole is potentially a useful probe for amplifying differences in solution properties of tubulin subspecies.

Animals↗
PubMed1984

Thermodynamic linkages in rabbit muscle pyruvate kinase: kinetic, equilibrium, and structural studies.

The mechanism of allosteric regulation of rabbit muscle pyruvate kinase (PK) was examined in the presence of the allosteric inhibitor phenylalanine (Phe). Steady-state kinetic, equilibrium binding, and structural studies were conducted to provide a broad data base to establish a reasonable model for the interactions. Phe was shown to induce apparent cooperativity in the steady-state kinetic measurements at pH 7.5 and 23 degrees C. The apparent Km for phosphoenolpyruvate was shown to increase with increasing Phe concentrations. These results imply that Phe reduces the affinity of PK for phosphoenolpyruvate. This conclusion was substantiated by equilibrium binding studies which yielded association constants of phosphoenolpyruvate as a function of Phe concentration. The binding constant of Phe was also determined at pH 7.0 and 23 degrees C. The effect of ligands on the hydrodynamic properties of PK was monitored by difference sedimentation velocity, sedimentation velocity, and equilibrium experiments. The results showed that PK remains tetrameric both in the presence and in the absence of Phe. However, Phe induces a small decrease in the sedimentation coefficient of the enzyme; hence, it suggests a loosening of the protein structure. The accessibility of the sulfhydryl residues of the enzyme also increases in the presence of Phe. Furthermore, the Phe-induced conformational change was approximately 90% complete when only 25% of the binding sites were saturated. This result suggested that the regulatory behavior of PK might satisfactorily be described by the two-state model of Monod-Wyman-Changeux [Monod, J., Wyman, J., & Changeux, J.-P. (1965) J. Mol. Biol. 12, 88-118].

Allosteric Site↗
PubMed1981

Preferential solvent interactions between proteins and polyethylene glycols.

Preferential solvent interactions between polyethylene glycols and five proteins were investigated by density measurements and analyzed by the multicomponent theory. These measurements were conducted as a function of concentration and molecular size of the synthetic polymer at different pH values. The results showed that proteins are preferentially hydrated under the experimental conditions employed, i.e. polyethylene glycol is excluded from the protein domain. The introduction of protein thermodynamically destabilizes the solvent system. The magnitude of instability increases with increasing concentration of the polymer. Furthermore, systems of polyethylene glycols of higher molecular weight are more destabilized. A linear relationship was observed between the magnitude of destabilization and average hydrophobicity of the proteins employed with the exception of tubulin. The system is more destabilized in the presence of proteins with higher content of hydrophilic residues indicating that the interaction between polyethylene glycol and ionized residues is thermodynamically unfavorable with a negative ion being more so than a positive one. After correcting for the contribution of ionic effect on the instability of the system it was found that at least for a protein of average hydrophobicity of 1000 cal/residue the mass of the protein contributes to the instability also. It may, therefore, be concluded that in a polyethylene glycol system the presence of protein leads to unfavorable thermodynamic interaction which in turn leads to phase separation. The causes of such unfavorable interaction include the charges residing on the protein.

Animals↗
PubMed1980

Effects of nocodazole on structures of calf brain tubulin.

The interaction of nocodazole with calf brain tubulin was studied to determine the effect of such interaction on the structure of tubulin. The effect of nocodazole on the self-association of tubulin was monitored by turbidity measurements and velocity sedimentation. Sedimentation patterns indicate that nocodazole neither induces tubulin to undergo self-association to form higher orders of aggregate nor does it perturb the equilibrium of the reaction leading to the formation of 42S double-ring structures although nocodazole binds to both the tubulin dimers and the polymeric form. Nocodazole does, however, inhibit the in vitro reconstitution of microtubules, and the presence of microtubule-associated proteins does not amplify the inhibitory effect of the drug. The conformational changes in tubulin upon binding of nocodazole were monitored by differential spectroscopy, circular dichroism, fluorescence, and chemical modification of sulfhydryl residues. Results from these studies show that the sulfhydryl residues become more accessible to chemical modification. In contrast, the binding of nocodazole does not significantly alter the net environment of tryptophan chromophores. These residues are apparently not all located on the surface of the tubulin molecule and at least some are partially buried.

Animals↗