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Biomedical subjects

R H Matthews

Publications and source records attributed to R H Matthews.

45 records · Page 3Linked to original sources
PubMed1975

Biphasic kinetic plots and specific analogs distinguishing and describing amino acid transport sites in S37 ascites tumor cells.

Curve-fitting procedures indicated that exo-2-amino-bicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) modified V and Km for one of two systems serving for histidine transport into the S37 ascites tumor cells. When this system was obliterated by leucine in the medium, BCH had no effect on histidine transport. Curve-fitting procedures similarly suggest N-methyl-alpha-aminoisobutyric acid affected the Km and V values for the other histidine-transporting system and that carboxymethylhistidine (His(Cm)) inhibited both transport systems. His(Cm) further inhibited histidine uptake into leucine-inhibited cells. Km and V values were altered simultaneously in the presence of several inhibitory analogs. Alanine methyl ester markedly inhibited high-concentration histidine uptake, whereas leucine methyl ester markedly inhibited low-concentration histidine uptake. The present results confirm earlier suggestions that our high c system is Christensen's A system and our low c system his L system. We also confirm a very high degree of specificity of N-methyl-alpha-aminoisobutyric acid for the A or high c system, and of BCH for the L or low c system. We suggest the utility of combining two approaches to the study of transport system properties; use of specific analogs and modification of biphasic plots. We demonstrate that the carboxyl group is not a prerequisite molecular feature for inhibitory interaction with the A or L system.

Alanine↗
PubMed1973

Kinetics of the processes of desorption from fatty acid monolayers.

The surface area, A, of contracting fatty acid monolayers was measured as a function of time, t, at constant surface pressure. In the initial temporal phase, ln A was linear with radical t. In a subsequent steady-state phase, ln A was linear with t. The initial desorption coefficient for sodium palmitate, K(i), and the steady-state desorption coefficient, K(s), varied directly with surface pressure and subphase pH, and these desorption coefficients also varied with the composition of the subphase buffer. However, the K(s)/K(i) ratio was independent of these variables. The diffusion coefficient, D(25), for sodium palmitate calculated from desorption coefficient ratios was 4.8 +/- 0.6 x 10(-6) cm(2)/sec. This value was in reasonable agreement with D(25) for sodium palmitate measured by time-lag diffusion, 3.7 +/- 0.6 x 10(-6) cm(2)/sec. D(25) values obtained for a series of fatty acids suggested that higher members of the series diffused as small aggregates averaging two to four molecules in size. Kinetic and diffusion data both supported a model for the desorption process described by Ter Minassian-Saraga.

Chemical Phenomena↗
PubMed1972

Effect of ionization and cation selectivity on the expansion of stearic acid monolayers.

Force-area isotherms of stearic acid and stearic acid-stearyl alcohol mixtures were investigated on alkaline subphases that contained Tris, Na(+), or K(+) cations and that varied in pH and ionic strength. The monolayer behaved as though ionization was effectively complete in the expanded region of the force-area isotherm. Surface pressure in this region was independent of pH and varied inversely with ionic strength as predicted by the Davies equation. The monolayer behaved as a partially ionized film in the plateau region of the force-area isotherm. Surface pressure in this region varied directly with pH and ionic strength as predicted by a modified Davies equation for partially ionized monolayers. The neutral molecule, stearyl alcohol, exerted a large condensing effect on the ionized film at pH 12.8, and this condensing effect also supported the concept that a partially ionized stearic acid film existed in the plateau region of the force-area isotherm. A greater binding affinity for Na(+) than for K(+) showed that the stearate anion surface behaved as a strong field at pH 10 and above, and a greater binding affinity for K(+) than for Na(+) showed that the stearate anion surface behaved as a weak field at pH 9. The weak field explained in part the anomalous binding affinity of the large Tris cation for the stearate monolayer at pH 9.

Buffers↗
PubMedDate not supplied

[14C]leucine chloromethylketone interaction with sarcoma 37 cell plasma membrane components.

Leucine chloromethylketone labeling of viable S37 cells was preferential for the plasma membrane fraction. The pattern of radiolabeling of the plasma membrane proteins was time dependent. After 5 min the radiolabel was localized with glutamyl transpeptidase, and subsequently with other physiologically active proteins as a function of time after incubation. Labeling of proteins was temperature dependent and incubation of viable S37 cells with the radiolabeled substrate at 0 degrees C yielded little or no radioactivity localized in the plasma membrane. The molecular weight of one radiolabeled substrate--membrane protein complex was estimated on sodium dodecyl sulfate polyacrylamide gel electrophoresis to be between 100,000-200,000.

Amino Acid Chloromethyl Ketones↗