Drosophila acetylcholinesterase: effect of post-translational [correction of post-traductional] modifications on the production in the baculovirus system and substrate metabolization.

Acetylcholinesterase cDNAs from Drosophila melanogaster modified on its primary sequence were cloned into baculovirus and were expressed in Sf9 cells with the aim to identify a mutant form that produces the enzyme at a high level. Directed mutagenesis was used in order to independently knockout different sites of post-translational modifications: exchange of the C-terminal hydrophobic peptide for a glycolipid molecule, dimerization by disulfide bridge, N-linked glycosylation at the five accessible sites, and subunit formation by proteolytic cleavage of a hydrophilic peptide found in the precursor. Another mutation involved the elimination of a free cysteine in the mature protein. All mutations involving post-translational modifications resulted in lower recoveries, suggesting that they are useful for maintaining high amounts of protein in the synapse. By contrast, elimination of a free cysteine in the mature protein permitted an increase in the level of production of the enzyme. These mutations did not affect specific activity of the enzyme at substrate concentrations ranging from 3 microM to 200 mM, suggesting that activation and inhibition of the enzyme activity does not originate from a polymorphism in post-translational modifications.

Phosphotyrosine phosphatase activity and haematologic changes in Down's syndrome patients.

Assays of neutrophil phosphotyrosine phosphatase activity and determination of haematological parameters were performed on 12 trisomic 21 probands without any clinical or biological symptom of other evolutive disease. Haematological studies showed the two main classical abnormalities: the existence of a macrocytosis and an enhanced lymphocyte count. Of interest are the very reduced rates of phosphotyrosine phosphatase activity found in granulocytes from these patients. This defect in protein phosphatase can be considered as an additional enzymatic change extending the list of modified factors recognized at molecular and cellular levels in subjects whose risk of leukaemia is significantly increased.

[Specificity and reversibility of insulin binding to isolated thyroid nuclei]. / Spécificité et réversibilité de la liaison de l'insuline aux noyaux isolés thyroïdiens.

Inhibition studies of nuclear binding of labelled insulin by unlabelled insulin, proinsulin and polypeptide hormones (glucagon, GH, TSH) as well as kinetics of binding dissociation suggest that thyroid isolated nuclei specifically, at least pro parte, and reversibly bind to insulin.

[Presence of nuclear triiodothyronine (T3) receptors in mouse fibroblasts]. / Présence de récepteurs nucléaires à la triiodothyronine (T3) dans le fibroblaste de souris.

The present preliminary data obtained from intact fibroblasts of adult mice (polyploid stem L 929) suggest that this cell system possesses high-affinity and saturable nuclear binding sites for triiodothyronine. As estimated by the Scatchard analysis, the equilibrium dissociation constant is approximately 2 X 10(-10) moles, the maximal binding capacity is about 2 000 sites for T3 per cell nucleus.