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PubMed1980

Lipid interactions with human alpha-fetoprotein (AFP). A study of the role of such interactions in the ability of human AFP to suppress lymphocyte transformation.

The ability of human alpha-fetoprotein (HAFP) isolates to inhibit human lymphocyte transformation varies over 2-3 orders of magnitude. Since HAFP is known to bind fatty acids, we have examined the possible role of lipid binding in producing this variability. While certain oxygenated sterols are potent inhibitors of lymphocyte transformation, and while the kinetics of such inhibition precisely mimic those of HAFP, HAFP is, by contrast, a weak inhibitor of sterol synthesis in mitogen-stimulated human lymphocytes. Fatty acids (18:0, 18:1, 18:2, 18:3, 20:4, 22:6) and 10(-4) M have little or no effect upon lymphocyte transformation. The fatty acid content of seen HAFP isolates ranged from 2.3 to 8.0 mol fatty acid/mol HAFP and included 12:0, 14:0, 16:0 (the most abundant), 18:0, 20:4, and 22:0; no 22:6 was found. There was no correlation between the total or individual fatty acid contents of HAFPs and their ability to inhibit lymphocyte transformation. Lysooleoyl-, lysostearoyl-, and lysopalmitoyl-lecithin at 5 X 10(-5) M all inhibited lymphocyte transformation (30.1%, 52.1%, and 58.1%, respectively) and the latter was active at 6.3 X 10(-6) M. Exposure of HAFP to a 5-fold molar excess of [14C]-lysopalmitoyl lecithin resulted in significant (10%) binding to HAFP, while no significant binding of dipalmitoyl lecithin occurred under similar conditions. Analysis of lipid extracts of potent HAFP isolates by thin-layer chromatography failed to reveal the presence of phospholipids. Although HAFP can bind certain lipids, and although certain lipids inhibit lymphocyte transformation, we conclude that HAFP suppression of lymphocyte transformation cannot be attributed to the binding of hydrocortisone, prostaglandins, fatty acids, lysolecithins, or oxygenated sterol compounds.

Chemical Phenomena↗
PubMed1983

[Intercellular relay interactions in explants of amphibian embryonic tissues. I. Intercellular relay interactions in normal explant morphogenesis].

In the explants of lateral mesoderm, together or without the overlaying ectoderm, taken from the neurula-early tail bud of amphibian embryos (Xenopus laevis, Rana temporaria) within 5-30 min, several types of cytological transformations have been observed, some of these being: formation of a microfilamentous layer under the naked explant surface, morphological polarization, and unilateral spreading of cells. These processes are described at the light and electron microscopy levels. It is suggested that these may be of relay character, that is, each transformed cell induces the same transformation in the adjacent one. The cytological transformations are correlated with metabolic ones described elsewhere.

Animals↗
PubMed1976

Thyroxine-protein interactions. Interaction of thyroxine and triiodothyronine with human thyroxine-binding globulin.

The effect of temperature on the binding of thyroxine and triiodothyronine to thyroxine-binding globulin has been studied by equilibrium dialysis. Inclusion of ovalbumin in the dialysis mixture stabilized thyroxine-binding globulin against losses in binding activity which had been found to occur during equilibrium dialysis. Ovalbumin by itself bound the thyroid hormones very weakly and its binding could be neglected when analyzing the experimental results. At pH 7.4 and 37 degrees in 0.06 M potassium phosphate/0.7 mM EDTA buffer, thyroxine was bound to thyroxine-binding globulin at a single binding site with apparent association constants: at 5 degrees, K = 4.73 +/- 0.38 X 10(10) M-1; at 25 degrees, K = 1.55 +/- 0.17 X 10(10) M-1; and at 37 degrees, K = 9.08 +/- 0.62 X 10(9) M-1. Scatchard plots of the binding data for triiodothyronine indicated that the binding of this compound to thyroxine-binding globulin was more complex than that found for thyroxine. The data for triiodothyronine binding could be fitted by asuming the existence of two different classes of binding sites. At 5 degrees and pH 7.4 nonlinear regression analysis of the data yielded the values n1 = 1.04 +/- 0.10, K1 = 3.35 +/- 0.63 X 10(9) M-1 and n2 = 1.40 +/- 0.08, K2 = 0.69 +/- 0.20 X 10(8) M-1. At 25 degrees, the values for the binding constants were n1 = 1.04 +/- 0.38, K1 = 6.5 +/- 2.8 X 10(8) M-1 and n2 = 0.77 +/- 0.22, K2 = 0.43 +/- 0.62 X 10(8) M-1. At 37 degrees where less curvature was observed, the estimated binding constants were n1 = 1.02 +/- 0.06, K1 = 4.32 +/- 0.59 X 10(8) M-1 and n2K2 = 0.056 +/- 0.012 X 10(8) M-1. When n1 was fixed at 1, the resulting values obtained for the other three binding constants were at 25 degrees, K1 = 6.12 +/- 0.35 X 10(8) M-1, n2 = 0.72 +/- 0.18, K2 = 0.73 +/- 0.36 X 10(8) M-1; and at 37 degrees K1 = 3.80 +/- 0.22 X 10(8) M-1, n2 = 0.44 +/- 0.22, and K2 = 0.43 +/- 0.38 X 10(8) M-1. The thermodynamic values for thyroxine binding to thyroxine-binding globulin at 37 degrees and pH 7.4 were deltaG0 = -14.1 kcal/mole, deltaH0 = -8.96 kcal/mole, and deltaS0 = +16.7 cal degree-1 mole-1. For triiodothyronine at 37 degrees, the thermodynamic values for binding at the primary binding site were deltaG0 = -12.3 kcal/mole, deltaH0 = -11.9 kcal/mole, and deltaS0 = +1.4 cal degree-1 mole-1. Measurement of the pH dependence of binding indicated that both thyroxine and triiodothyronine were bound maximally in the region of physiological pH, pH 6.8 to 7.7.

Binding Sites↗
PubMed1984

Interaction of Mg2+ with human liver aldehyde dehydrogenase. II. Mechanism and site of interaction.

The dehydrogenase reaction of the cytoplasmic isozyme (E1) of human aldehyde dehydrogenase (EC 1.2.1.3) was inhibited while that of the mitochondrial isozyme (E2) was stimulated by low levels of Mg2+ (up to about 150 microM). However, with respect to esterase activity, Mg2+ had a similar effect on both isozymes in that only the NADH-stimulated reaction was effected. Comparison of coenzyme dissociation constants from the dehydrogenase reaction with the coenzyme stimulation constants from the esterase reactions provided the detailed mechanism of the action of Mg2+. The data indicate that Mg2+ acts similarly to bring about alterations in the activity of both isozymes. With E1, where NADH release is the rate-determining step, Mg2+ inhibits by causing a tighter binding of NADH to the enzyme. With E2, however, the stimulation results from the increased rate of acid release from the ternary complex (rate-determining step for E2) when Mg2+ is also present. These results suggest that three enzyme conformers participate in the dehydrogenase reaction and provide a unified mechanism for the stimulation of the dehydrogenase reaction catalyzed by the E2 isozyme, inhibition of the same reaction catalyzed by the E1 isozyme, and the effects of Mg2+ on the esterase reactions (nonstimulated and coenzyme stimulated) of both isozymes.

Aldehyde Dehydrogenase↗
PubMedDate not supplied

Analysis of specific interactions influenza virus and cells of different sensitivity. Note 2. Characteristics of influenza virus-host cell interaction in persistent infection.

Molecular hybridization was used for the demonstration of virus-specific RNA synthesis in the latent phase of influenza virus replication in the sensitive MDCK cell cultures and for its investigation in the persistent system represented by nonpermissive AO cells and influenza A/Victoria 35/72 (H3N2).

Amnion↗