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Y Jacques

Publications and source records attributed to Y Jacques.

122 records · Page 7Linked to original sources
PubMed1978

The role of serum albumin in the uptake of fatty acids by cultured cardiac cells from chick embryo.

Fatty acids enter the cultured cardiac cells from chicken embryo through two mechanisms, one involving a saturable process, the other resembling passive diffusion. Studies of the saturable component, at fixed concentrations of palmitate or of oleate and at increasing concentrations of albumin, show that this protein increases the rate of palmitate uptake with a maximum at palmitate/albumin molar ratios between 7 and 10 while it decreases the rate of oleate uptake under all conditions. Albumin cannot be replaced by other serum proteins; its effect is specific to saturated fatty acids, can be mimicked by the detergent Tween 40 and involves the binding of the fatty acid to the protein, prior to its delivery to the cell. Both with labelled saturated and unsaturated fatty acids the presence of albumin lowers the proportion of unesterified fatty acids and enhances the proportion of esterified fatty acids recovered in the cardiac cell after uptake. A similar effect of albumin was also found with hepatocytes and permanent cell lines. A specific role for serum albumin is presented, which assumes a 'dispersing' effect of this protein towards dimers (or higher aggregates) of saturated fatty acids and the entry of fatty acids into the cell as monomers.

Animals↗
PubMed1977

Interrelation between transfer RNA and amino-acid-activating sites of methionyl transfer RNA synthetase from Escherichia coli.

Binding of tRNA(Met/f) to the monomeric trypsin-modified methionyl-tRNA synthetase turns off the methionine-dependent isotopic ATP--PPi exchange. In the case of the dimeric native methionyltRNA synthetase, one anticooperatively bound tRNA(Met/f) inhibits the exchange by only 50%. These behaviours of tRNA do not require the integrity of the 3'-terminal adenosine. Esterification by methionine of the 3' end of tRNA reinforces the affinity of tRNA(Met/f)for the enzymes. In the case of the native enzyme, due to this effect, a second binding mode for methionyl-tRNA may be demonstrated through the isotopic exchange. This additional binding of tRNA corresponds to the expression of the anticooperatively blocked tRNA binding site. Methionine reverses competitively the reinforcing effect of the esterified methionyl moiety on tRNA binding. It is concluded that after esterification of tRNA, the aminoacyl residue still binds the enzyme, probably within the methionine activating site. The latter behaviour may account for the observation that excess methionine accelerates the aminoacylation turnover rate of tRNA(Met/f).

Adenosine Triphosphate↗
PubMed1976

Methionyl-tRNA synthetase from Escherichia coli: active stoichiometry and stopped-flow analysis of methionyl adenylate formaiton.

Native dimeric methionyl-tRNA synthetase and its monomeric proteolytic fragment are shown to form and to bind 1 mol of methyionyl adenylate per polypeptide chain. Moreover, at 25 degrees C, each monomer of the dimeric native enzyme behaves independently, exhibiting the same parameters for the methionine activation reaction as does the monomeric modified enzyme. These results were obtained using several independent methods including equilibrium and nonequilibrium dialysis, active site and tryptophan fluorescence titrations, and stopped-flow by fluorescence. Stopped-flow resolution of the reversible methionine activation reaction also demonstrates that methionine and ATP-Mg2+ react without coupling to form a ternary enzyme-methionine-ATP-Mg2+ complex. This complex readily converts to enzyme-methionyl approximately adenylate-PP-Mg2+ with a standard free energy close to zero. It is concluded that the uncoupled enzyme-methionine-ATP-Mg2+ complex may resemble the transition state of the reaction at the expense of the additional state of the reaction at the expense of the additional synergistic binding energy provided by reciprocal coupling, within the site, of the methionine molecule with the adenosine and PP-Mg2+ parts of the ATP-Mg2+ molecule (Blanguet, S., Fayat, G., and Waller, J. P. (1975), J. Mol. Biol. 94, 1.).

Adenosine Monophosphate↗
PubMed1976

The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K-12. Incubation of the enzyme in alkaline conditions: dissociation and disulfide-bridge formation.

Aspartokinase I - homoserine dehydrogenase I from Escherichia coli K-12, a homotetrameric enzyme, dissociates into dimers upon alkaline treatment. Both aspartokinase and homoserine dehydrogenase inactivation, as well as desensitazion towards L-threonine, occur in a multi-step process. Dithiothreitol stabilizes a dimeric form retaining full activity and sensitivity; L-homoserine stabilizing another dimeric form devoid of aspartokinase activity and retaining a substantial dehydrogenase activity insensitive toward L-threonine. A model is proposed showing that dissociation into dimers occurs in a first step, the resulting dimer losing both aspartokinase and homoserine dehydrogenase sensitivity in two subsequent steps involving the formation of intrachain disulfide bonds.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Capacity of alloreactive human T clones to produce factor(s) inducing proliferation of the IL3-dependent DA-1 murine cell line. I. Evidence that this production is under IL2 control.

Several T-lymphocyte clones obtained from rejected human kidney allografts and maintained for several months in recombinant IL2 and antigen-supplemented cultures were studied for their capacity to produce lymphokines in vitro. Six clones produced a factor able to increase 3HTdR uptake of the IL3-dependent DA-1 murine cell line. All were T4+, T3+ and T11+ and fitted with a probability of monoclonality above 97%. The factor, designated as human-interleukin-DA (HILDA), was not produced when autologous EBV-transformed B cells were added in the culture in the absence of exogenous IL2. Addition of pure recombinant IL2 along with donor EBV-transformed cell lines resulted in a sharp increase in HILDA yield, whereas a low amount of this factor was also produced with the autologous EBV B lymphocyte in the presence of exogenous IL2. Kinetics studies show that HILDA was detectable as early as 24 to 48 h, peaked at day 3 and plateaued until day 5. The antigen-exogenous IL2-driven pathway of HILDA production by clones was bypassed by use of either PMA or calcium ionophore (CaI) alone or associated in the culture. Both compounds induced dose-related HILDA production (without antigen and/or exogenous IL2). No synergistic effect of PMA and CaI was noted, although an additional effect could be seen when a suboptimal dose of CaI was used.

Animals↗
PubMedDate not supplied

Negative regulation of onconstatin M signaling by suppressor of cytokine signaling (SOCS-3).

Oncostatin M (OSM) is known to inhibit the growth of melanocytes and early-stage melanomas, but this ability is lost with melanoma progression. The biological effects of OSM involve the activation of Janus kinases (Jak) and signal transducer and activator of transcription (STAT) factors. Since SOCS (suppressor of cytokine signaling) a recently described family of regulatory proteins, has been shown to act through down-regulation of Jak-STAT signaling, we investigated their putative role in the inhibition of OSM signaling in the human melanoma cell line A375. We observed that, among the SOCS family members examined, only SOCS-3 mRNA was strongly and rapidly induced by OSM. SOCS-3 protein was present within 1h and rapidly declined thereafter. Constitutive expression of SOCS-3 protein completely abolished the activation of the Jak-STAT signaling pathway as well as the Ras-MAP kinase pathway. As a result, A375 cells acquired an OSM-resistant phenotype. Our findings demonstrate that SOCS-3 is a potent regulator of OSM response and suggest that dysregulation of SOCS-3 expression could provide a mechanism for OSM resistance acquisition during tumour progression.

Base Sequence↗
PubMedDate not supplied

Effect of recombinant interferon gamma and interleukin-2 and of a monoclonal antibody against interferon gamma on the rat immune response against heart allografts.

We studied the effect of rat rec-IFN-gamma, human rec-IL-2, and an IgG1 monoclonal antibody (DB1) directed against rat IFN-gamma on allograft survival in the rat in various experimental conditions. The DB1 monoclonal antibody did not prolong heart allograft survival in the (LEW/BN)F1 to LEW combination, even when used at high doses (2 mg/rat x 9 days). Rec-IFN-gamma induced major histocompatibility antigen expression in vivo, but its administration had no effect on the graft survival either of untreated LEW recipients of (LEW x BN)F1 heart allografts or of donor blood-transfused LEW recipients. In addition, rec-IFN-gamma alone had no effect on graft survival in cyclosporine-treated rats. In contrast, rec-IL-2 shortened heart allograft survival both in untreated and in cyclosporine-treated recipients. Rec-IFN-gamma partially reversed the effects of rec-IL-2 in cyclosporine-treated rats. The data suggest that in vivo administration of IFN-gamma in allograft recipients may have a suppressor effect, in addition to the postulated augmenting effect on the immune response by increasing MHC antigen expression.

Animals↗
PubMedDate not supplied

[Isotope lymphography and its therapeutic implications].

Radiological lymphography presents drawbacks among which the risk of aggravation of the edema is most prominent. The authors report their experience with isotopic lymphography which best reproduces the physiological conditions of lymphatic drainage; it provides informations on the dermal or canalicular drainage route, the possible peripheral stasis or lymph leakage.

Adult↗