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D J Gordon

Publications and source records attributed to D J Gordon.

80 records · Page 5Linked to original sources
PubMed1977

Interaction between Acanthamoeba actin and rabbit skeletal muscle tropomyosin.

The binding of 125I-labeled muscle tropomyosin to Acanthamoeba and muscle actin was studied by ultracentrifugation and by the effect of tropomyosin on the actin-activated muscle heavy meromyosin ATPase activity. Binding of muscle tropomyosin to Acanthamoeba actin was much weaker than its binding to muscle actin. For example, at 5 mM MgCl2, 2 mM ATP, and 5 micronM actin, tropomyosin bound strongly to muscle actin but not detectably to Acanthamoeba actin. When the concentration of actin was raised from 5 micronM to 24 micronM in the presence of 80 mM KCl, the binding of tropomyosin to Acanthamoeba actin approached its binding to muscle actin. As with muscle actin, the addition of muscle heavy meromyosin in the absence of ATP induced binding of tropomyosin in Acanthamoeba actin under conditions were binding would otherwise not have occurred. The most striking difference between the interactions of muscle tropomyosin with the two actins, however, was that under conditions where tropomyosin was found to both actins, its stimulated the Acanthamoeba actin-activated heavy meromyosin ATPase but inhibited the muscle actin-activated heavy meromyosin ATPase.

Actins↗
PubMed1976

Polymerization of Acanthamoeba actin. Kinetics, thermodynamics, and co-polymerization with muscle actin.

The kinetics and thermodynamics for the polymerization of purified Acanthamoeba actin were studied and compared to muscle actin. Polymerization was qualitatively similar for the two actins with a rate-limiting nucleation step followed by rapid polymer extension. Polymerization occurred only above a threshold critical concentration which varied with polymerization conditions for each actin. In the presence of 2 mM MgCl2, nucleation of both actins was rapid and their critical concentrations were similarly low and not detectably dependent on temperature. In 0.1 M KCl, the rates of nucleation of both actins were much slower than when Mg2+ was present and were significantly different from each other. Also, under these conditions, the critical concentrations of Acanthamoeba and muscle actin were significantly different and both varied markedly with temperature. These quantitative differences between the two actins could be attributed to differences in both their enthalpies and entropies of polymerization, Acanthamoeba actin having the more positive deltaH and delta S. Co-polymerization of the two actins was also demonstrated. Overall, however, there were no qualitative differences between Acanthamoeba and muscle actin that would suggest a unique role for the monomer-polymer equilibrium of cytoplasmic actin in cell motility.

Actins↗
PubMed1976

Characterization of cytoplasmic actin isolated from Acanthamoeba castellanii by a new method.

Cytoplasmic actin has been isolated from Acanthamoeba castellanii by a new method, employing chromatography on DEAE-cellulose, that improves the yield by more than 20-fold over the previously reported method. This procedure should be particularly useful for isolating actin from cells in which it is present in relatively low concentration because the method does not depend initially on the polymerization of actin or its interaction with myosin. Systematic comparison of the properties of purified Acanthamoeba actin and rabbit skeletal muscle actin shows them to be similar in many ways: viscosity of F-actin, stoichiometry of bound nucleotide, stoichiometry of binding of muscle heavy meromyosin and myosin subfragment 1 in the absence of ATP, and ability to inhibit the KATPase activity of heavy meromyosin. The amino acid compositions of Acanthamoeba and muscle actin are also quite similar, but significant differences, especially the presence of epsilon-N-methyllysines in Acanthamoeba actin, have been confirmed. In addition to this structural difference, we find that Acanthamoeba actin is only one-third as effective as muscle actin as an activator of the MgATPase of muscle heavy meromyosin and subfragment 1. For Acanthamoeba actin, as for muscle actin, this activation exhibits hyperbolic dependence on actin concentration; i.e. the double reciprocal plot of ATPase activation versus actin concentration is linear. From these plots we find that the two actins give the same extrapolated ATPase activity at infinite actin concentration (Vmax) but differ by a factor of three in the concentration of actin needed to produce half-maximal activation (Kapp).

Actins↗
PubMed1971

Optical activity of membrane suspensions: calculation of artifacts by Mie scattering theory.

The circular dichroism, optical rotatory dispersion, and optical density of a suspension of erythrocyte ghosts are calculated from the measured optical properties of solubilized ghosts by classical general scattering theory (Mie theory). The ghost is represented by a solvent-filled spherical shell 7 nm (70 A) thick and 3.5 mum in radius. The 3- to 5-nm red shifts and unusual band shapes observed in the circular dichroism and optical rotary dispersion of suspensions of the intact ghosts, but not in the solubilized membranes, are reproduced by these calculations. Both differential absorption and differential scattering of left-and right-circularly polarized light contribute significantly to the calculated circular dichroism spectra. The artifacts of small membrane vesicles are shown to be less than those of intact ghosts. It is concluded that the characteristic anomalies in the optical activity of membrane suspensions are artifactual.

Cell Membrane↗
PubMedDate not supplied

Dietary determinants of plasma cholesterol change in the recruitment phase of the Lipid Research Clinics Coronary Primary Prevention Trial.

We have investigated the relationship of diet to plasma lipid and lipoprotein levels in 6494 hypercholesterolemic (Type IIA) men who were instructed in an isocaloric, 400 mg cholesterol, 0.8 polyunsaturated-to-saturated fat ratio diet in the course of recruitment for the Lipid Research Clinics Coronary Primary Prevention Trial. Single 24-hour dietary recalls, plasma total and high density lipoprotein cholesterol, and total triglyceride determinations were obtained approximately 1 month before and 1 month after dietary instruction. Cross-sectional correlation analysis disclosed no significant association between diet and plasma cholesterol at entry. However, when diet-associated changes were similarly analyzed, weight loss, decreased intakes of saturated fat and cholesterol, and increased intake of polyunsaturated fat were all significantly and independently predictive of falls in plasma cholesterol, mainly in its low density lipoprotein fraction. The multiple correlation coefficient for the resultant four-variable regression model was 0.29. Diet-associated changes in plasma very low density lipoprotein cholesterol were less marked but in the same direction. These dietary changes were also weakly associated with a lowering of plasma high density lipoprotein cholesterol, while weight loss had an opposite effect of similar strength. When one takes into account the variability of dietary recall data, the observed diet-associated changes in plasma cholesterol were compatible with the findings of metabolic ward studies.

Adult↗