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Biomedical subjects

J Eckel

Publications and source records attributed to J Eckel.

74 records · Page 5Linked to original sources
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Insulin receptors on isolated heart cells: effect of temperature and hydrolytic enzymes.

Isolated muscle cells from adult rat heart have been used to study the effect of temperature and enzymic digestion on the binding of 125I-labelled insulin. Equilibrium binding studies were performed at both 4 and 37 degrees C, using insulin concentrations ranging from 2.5 X 10(-11) mol/l to 10(-6) mol/l. The empty site affinity constant decreased by 51% from 1.0 X 10(8) l/mol at 4 degrees C to 4.9 X 10(7) l/mol at 37 degrees C, whereas the total receptor concentration remained unaltered at both temperatures. The rate of dilution induced dissociation was enhanced by the presence of native insulin at 37 degrees C, confirming the presence of negative cooperativity among the receptor sites at physiological temperatures. Treatment of isolated heart cells with trypsin and beta-galactosidase led to a decrease in specific binding of 125I-labelled insulin. Myocytes treated with neuraminidase exhibited a significant increase in insulin binding, which was shown to be due to an increase in insulin-receptor affinity. These studies provide new information on the molecular characteristics of insulin receptors in the heart muscle.

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PubMedDate not supplied

Identification and characterization of a novel variant in the highly conserved catalytic center of Rab11a.

Small GTPases of the Rab family regulate vesicular traffic and distribution of proteins in different cell types. Rab11a is a member of this GTP hydrolyzing protein class and acts as a mediator of insulin stimulated translocation of the glucose transporter GLUT4 in peripheral tissues including heart and skeletal muscle. Here we report on Rab11a Q70R, a mutation in the catalytic center of Rab11a, observed in the cardiomyoblast cell line H9c2. Analysis of GTPase activity showed that Rab11a Q70L acts as a classical constitutive active mutant. Interestingly, the GTPase activity of Rab11a Q70R was not significantly different from the enzymatic activity of the Rab11a Q70 wild type protein. We therefore conclude that the glutamine residue of Rab11a at position 70 is not strictly essential for GTPase activity of this protein in contrast to Ras and other Rab proteins.

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