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Biomedical subjects

Y Eilam

Publications and source records attributed to Y Eilam.

64 records · Page 4Linked to original sources
PubMed1976

The mechanism of interaction between high-affinity probes and the uridine transport system of mammalian cells.

The carrier of uridine transport in hamster cells in culture is highly susceptible to the inhibitory effect of probes like S-benzylated derivatives of mercaptopurine nucleosides. The interaction between the probes and the carrier is competitive and reversible and it takes place at a site different from the substrate binding site. The Ki for the most potent derivative p-nitrobenzyl-6-mercaptoinosine is 0.15 n Molar at 20 degrees C. The effect of the probes is interpreted in terms of conformational change induced on the carrier upon binding of the probe. The carrier assumes distinct conformations depending on whether it is probe-free (form A) or probe bound (form B). Kinetic as well as chemical evidence supports the predictions of the allosteric carrier model. A single component of kinetics is observed either in the absence of inhibitor (Km form A) or at high concentrations of inhibitor (Km form B). A two component kinetics is observed at intermediate concentrations of inhibitor (some carriers in form B and others in form A). The two forms have distinct Km values for uridine: form A50 muMolar and form B 250 muMolar. Two forms have also different susceptibilities to the action of organomercurials: form A is insensitive whereas form B is highly inhibited by the chemical modified of SH groups. The existence of putative allosteric sites in carriers is discussed in terms of modifier sites capable of modulating transport activities as a result of specific membrane-ligand interactions.

Allosteric Site↗
PubMed1975

Two-carrier models for mediated transport. II. Glucose and galactose equilibrium exchange experiments in human erythrocytes as a test for several two-carrier models.

1. Equilibrium exchange of glucose and of galactose is measured in human erythrocytes over wide concentration ranges. One-site Michaelis-Menten-type kinetics are shown for the two sugars. 2. In view of the results, two of the two-carrier models discussed in paper I (Eilam, Y. (1975) Biochim. Biophys. Acta 401, 349-363), the different sequential carriers and the antiparallel simultaneous carriers, are rejected for the sugar transfer system. The antiparallel sequential carriers model is consistent with these results.

Biological Transport↗
PubMed1973

A modle for active transport of sodium and potassium ions as mediated by a tetrameric enzyme.

A new model is proposed for the system that actively transports sodium and potassium ions across animal-cell membranes. The model is based on the physical and chemical properties of transport-associated adenosine triphosphatase (EC 3.6.1.3) and on the kinetics of ion movements mediated by the system. Transport is postulated to occur by internal transfer of cations across a protein tetramer embedded in the cell membrane. The protein tetramer can exist in either of two forms of identical energy; transport occurs as a result of the sequential "flipping" from one conformation to the other. The conformation change results in the interchanging of the affinities of cation-binding sites associated with different sub-units of the tetramer, with a concomitant splitting of adenosine triphosphate.

Adenosine Triphosphatases↗
PubMed1971

Ribosomes and Polysomes in Cucumber Leaves during Growth and Senescence.

The quantity of RNA in the ribosomal fraction of the first leaf of cucumber (Cucumis sativus) increases during growth, reaches a maximum before the final fresh weight is attained, and then decreases. The main changes are in the free ribosome fraction, the quantity of membrane-bound ribosomes remaining about constant. Few 65.5S chloroplast ribosomes are present in small leaves; however, they increase in quantity rapidly during growth and form about half of the ribosomes present in the mature fully green leaf. The cytoplasmic ribosomes have a sedimentation coefficient of 77.6S. Ribonuclease-sensitive polysomes were present in leaves of all ages except possibly the very oldest. The proportion of ribosomes in polysome form decreases during growth and then remains roughly constant during senescence. Following maturation of the leaf, the rate of incorporation of (32)P into ribosomal-fraction RNA begins to decline. This decline could account for the loss of ribosomes during the early stages of senescence. The possibility that leaf ribonuclease might be responsible for the final, more rapid loss of RNA, is discussed.

Journal Article↗