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Biomedical subjects

S H Lin

Publications and source records attributed to S H Lin.

At least 253 records · Page 14Linked to original sources
PubMed1982

Effect of cryosolvents and subzero temperatures on the hydrolysis of L-leucine-p-nitroanilide by porcine kidney leucine aminopeptidase.

The hydrolysis of L-leucine-p-nitroanilide by porcine kidney leucine aminopeptidase in aqueous mixed-solvent systems containing methanol, ethanol, dimethyl sulfoxide, and dimethylformamide has been investigated in the -30 to -23 degrees C temperature range. At 23 degrees C and pH* values in the 8-10 range, the enzyme is stable for over 25 h in solutions containing 50% v/v of any of these four cosolvents. Measurements of the tryptophan fluorescence of the enzyme at pH* 9.0 confirm that the enzyme is not denatured under these conditions. KM increases exponentially and kcat decreases linearly with increasing cosolvent concentration. Methanol, in particular, has a very small effect on KM. Ultrafiltration experiments demonstrate that there is no dissociation of monomers of the enzyme brought about by the presence of 50% v/v methanol or dimethyl sulfoxide. Preliminary tests with the partition method provide no evidence for an acyl-enzyme intermediate. The effect of pH* on kcat and KM in 50% v/v methanol is very similar to the effect of pH on these kinetic constants in aqueous solution. Lowering the temperature from 23 to 0 degree C does not alter the shape of the pH* profile obtained in 50% v/v methanol. The Arrhenius plot obtained in 50% v/v methanol is linear over the -30 to -23 degrees C temperature range, and the calculated energy of activation, 8.2 +/- 0.8 kcal/mol, is in good agreement with the value of 7.4 +/- 0.7 kcal/mol found for the reaction in aqueous solution. Collectively, these data indicate that methanol is the best cosolvent for cryoenzymological studies, that ethanol and dimethyl sulfoxide are also suitable cosolvents, and that the presence of any of these cosolvents at either ambient or subzero temperatures does not perturb the catalytic pathway.

Anilides↗
PubMed1982

Rate constant of vibrational redistribution in molecules using adiabatic approximation model.

By means of the proposed adiabatic approximation model for vibrational redistribution [Lin, S. H. (1980) Chem. Phys. Lett. 70, 492-499], the calculations of various rate constants caused by different couplings have been given in detail. By two methods it has been demonstrated that the rate constant caused by the Born-Oppenheimer mechanism, corrected by the non-Condon approximation, has the same order of magnitude as that contributed by the anharmonic mechanism. Furthermore, the important effect of molecular rotation on the rate constant based on the Coriolis coupling has been demonstrated.

Journal Article↗
PubMed1981

Metal binding stoichiometry and mechanism of metal ion modulation of the activity of porcine kidney leucine aminopeptidase.

Porcine kidney leucine aminopeptidase has been obtained from commercial sources as in inhomogeneous preparation with variable metal content and purified by affinity chromatography over L-leucylglycyl-AH-Sepharose. Treatment with Zn2+ followed by gel filtration restores the Zn2+ content of the native enzyme, which is 6 mol of Zn2+ per hexamer, each of which is located in a single catalytic binding site per subunit. The activity of the native enzyme is modulated by incubation with divalent metal ions; it is activated by Mn2+ and Mg2+ and inhibited by Ni2+, Cu2+, Zn2+, Hg2+ and Cd2+. These metals modulate the activity by binding to a separate site on each subunit, referred to as the regulatory site. Binding of these metals at the regulatory site alters the activity of the enzyme by changing kcat, leaving KM unaltered. The number and nature of the metal binding sites of porcine kidney leucine aminopeptidase are very similar to those of the enzyme from bovine lens.

Animals↗
PubMed1981

On the density matrix approach of intramolecular relaxation processes.

In this paper we derive the generalized master equations for the S(1) system coupled with the S(2) system, with the S(1) and S(2) systems embedded in a heat bath. This formalism can be applied to a number of problems like vibrational redistribution, dynamic effect of vibrational relaxation on electronic relaxation in condensed media, etc. In this paper the importance of the memory function associated with a relaxation process is emphasized.

Journal Article↗
PubMed1981

Quantum statistical mechanical theory of diffusion and reaction on solid surfaces.

We present the derivation of the general kinetic equations of diffusion and diffusion with interaction (or chemical reaction) on solid surfaces (or in dense media) by using the density matrix method. We indicate several problems to which this formalism applies and, in particular, discuss the damping effect on diffusion.

Journal Article↗
PubMed1981

Isolation and characterization of gonadotropin isohormones from the pituitary gland of pike eel (Muraenesox cinereus).

Pike eel gonadotropins were isolated from pituitary glands by 40% alcohol-6% ammonium acetate, pH 5.1 extraction and were purified by DEAE-cellulose chromatography and electrophoresis into four electrophoretically homogeneous forms. These four isohormones were biologically identified as gonadotropins by the stimulation of 32 P-uptake in 1 day-old chick testes, by the induction of ovulation in catfish, and by the in vitro production of testosterone from isolated rat Leydig cells and of androgen from carp testes. The amino acid composition of the isohormones were similar to other known piscine gonadotropins (carp and salmon) and were composed of two non-identical subunits with Tyr and Ser as N-terminal amino acid residues. The molecular weights of two subunits were 15000 and 10500, respectively, as estimated by SDS-gel disc electrophoresis.

Amino Acids↗
PubMed1980

Surface activities of tertiary amine local anesthetics at air/water interface in the presence and absence of phospholipid monolayers.

Adsorption of procaine and tetracaine to the dipalmitoyl phosphatidylcholine monolayers at the air/water interface is analyzed in terms of two types of interaction: (1) between the phospholipid molecules and the ligand molecules, and (2) among the ligand molecules themselves. The presence of the phospholipid monolayer increases the surface concentration of the anesthetics. The interaction energy, omega AB, between the phospholipid molecules and the anesthetic molecules at the interface accounts for this excess adsorption. The values were --2.95 kT for procaine and --2.99 kT for tetracaine where k is the Boltzmann constant and T = 298 K. The adsorption of the local anesthetics to the interface was cooperative. The interaction energy, omega AA, between the anesthetics molecules on the surface determines the cooperativity. The values were --0.056 kT for procaine and --0.397 kT for tetracaine, where T = 298 K. This parameter determines the slope of the curve plotted relating the surface concentration (gamma) and the logarithm of the bulk concentration (log C). When (omega AA/kT) greater than or equal to 1, the adsorption follows the phase-transition. A parameter KA, which is related to the difference of the free energy of anesthetics between the surface and the bulk molecules, locates the take-off point of the adsorption curve at the log C axis. The values were 2.15 x 10(3) for procaine and 7.00 x 10(3) for tetracaine. In spite of the general assumption that the difference in the clinical potency among local anesthetics are attributable to their lipid solubility, the present results showed that the phospholipid-anesthetic interaction energies for procaine and tetracaine were similar. The larger surface concentration of tetracaine than procaine at the same bulk concentration was due to the combined effect of KA and omega AA. KA represents the tendency of the anesthetic molecules to escape from the hydrogen-bonded water phase, and omega AA determines the cooperativity factor causing these molecules to aggregate at the interface. It was also observed that the charged forms of the anesthetics have non-zero surface activities.

Adsorption↗
PubMed1980

Wavelength regulation in rhodopsin: effects of dipoles and amino acid side chains.

The effects of dipoles and aromatic amino acid side-chain models on the absorption and optical activity of the rhodopsin chromophore were calculated by using perturbation theory, and the results were compared with those of a Pariser-Parr-Pople calculation for the unperturbed system. The interaction was assumed to result from purely electrostatic interactions. It was concluded that the side chains of phenylalanine and tryptophan should have no important effects. However, the charge separation in tyrosine is sufficient to cause substantial electrostatic perturbation; in fact, the effect of tyrosine is large enough to approximately many of the spectral properties of rhodopsin quantitatively. This is encouraging because the use of aromatic amino acid side-chain analogs probably provides a better physical model than the use of isolated full charges, except in the case of the counterion to the protonated Schiff base.

Chemical Phenomena↗
PubMed1980

Mechanisms of triboluminescence.

The purpose of this paper has been to develop the theoretical treatment of the triboexcitation mechanisms due to the electric field effect and the pressure effect and to show how to analyze the triboluminescent spectra to determine the external factors that affect or induce the triboluminescence.

Journal Article↗
PubMed1980

A theoretical study of resonance Raman scattering from molecules: High pressure effect.

The main purpose of this paper has been to study the high pressure effect on the resonance Raman scattering (RRS) of molecules in a dense medium. In deriving the RRS cross section under high pressure, a different approach from that presented in the previous papers has been used, and the resulting expression for the RRS cross section can be used to treat both pressure and temperature effects.

Journal Article↗
PubMed1979

Effect of molecular rotation on the vibration-vibration energy transfer in condensed media.

The purpose of the present communication has been to present the derivation of the vibrational relaxation rate constant for the case in which both phonons and the molecular rotation (three-dimensional) participate in the vibrational relaxation and to study the effect of molecular rotation on the vibration-vibration energy transfer in the condensed phase. The experimental results of vibration-vibration energy transfer between donors, NH and ND, and acceptors, CO and (13)CO, have been analyzed.

Journal Article↗
PubMed1979

A theory of light-induced explosion.

This paper presents a theoretical analysis, based on a simplified one-dimensional model, of the response of an explosive to a wide range of light intensities. A primary result has been the identification and development of a relationship among the important critical parameters. Numerical results illustrating the relationship among the critical light intensity, sample dimension, and ambient temperature have been obtained, with lead azide as the example.

Journal Article↗