On the relation of dystonic movements to serum thyroxine levels

A patient with psychomotor retardation secondary to delayed treatment of cretinism developed abnormal dystonic movements in the absence of other signs of toxicity during levothyroxine replacement therapy at a serum thyroxine level of 16 μg./100 ml. The dystonic movements disappeared when the serum thyroxine level fell. The abnormal movements were considered to be related to high thyroxine levels in this patient with pre-existing central nervous system dysfunction.     

Targeting of PP2A enzymes by viral proteins and cancer signalling

Protein phosphatase 2A (PP2A) is a large family of holoenzymes that comprises 1% of total cellular proteins and accounts for the majority of Ser/Thr phosphatase activity in eukaryotic cells. PP2A proteins are made of a core dimer, composed of a catalytic (C) subunit and a structural (A) subunit, in association with a third variable -regulatory (B) subunit. Although initially considered as a constitutive housekeeping enzyme, PP2A is indeed highly regulated by post-translational modifications of its catalytic subunit or by the identity of a regulatory type B subunit, which determines substrate specificity, subcellular localization and enzymatic activity of a defined holoenzyme. During the two last decades, multiple studies of structural and functional regulation of PP2A holoenzymes by viral proteins led to the identification of critical pathways for both viral biology and tumorigenesis. To date a dozen of different viruses (ADN/ARN or retrovirus) have been identified that encode viral proteins associated to PP2A. In this review, we analyze a biological strategy, used by various viruses based on the targeting of PP2A enzymes by viral proteins, in order to specifically deregulate cellular pathways of their hosts. The impact of such PP2A targeting for biomedical search, and in further therapeutic developments against cancer, will also be discussed.     

Succinobucol versus probucol: Higher efficiency of succinobucol in mitigating 3-NP-induced brain mitochondrial dysfunction and oxidative stress in vitro

This study evaluated and compared the potential protective effects of probucol and succinobucol, two lipid-lowering compounds with anti-inflammatory and antioxidant properties, on oxidative stress and mitochondrial dysfunction induced by 3-nitropropionic acid (3-NP, a succinate dehydrogenase (SDH) inhibitor largely used as model of Huntington's disease) in rat brain mitochondria-enriched synaptosomes. 3-NP caused significant inhibition of mitochondrial complex II activity, induced mitochondrial dysfunction and oxidative stress. Probucol and succinobucol prevented oxidative stress, but only succinobucol was able to prevent the mitochondrial dysfunction induced by 3-NP. Succinobucol, which did not recover complex II inhibition, was able to protect against 3-NP-induced decreased of MTT reduction, indicating that SDH is not the only enzyme responsible for MTT reduction. The present findings suggest that succinobucol might be a novel strategy to slow or halt oxidative events in neurodegenerative conditions.     

Partial amino acid sequence of two forms of human post-gamma-globulin.

We have purified two different electrophoretic forms of Post-γ-globulin defined by electrophoresis as “native slow” form and “fast” form respectively. Amino acid sequences of the first fifty-two residues of the “native slow” form and twenty-nine of the “fast” form were determined. The sequence shows that the “fast” form lacks the first nine amino acids of the “native slow” form.This observation is consistent with the existence of a “native slow” form that is degraded into other more acidic forms of Post-γ-globulin by loss of basic amino acids.     

Study on B-memory generation by Tnp-Ficoll: induction but not expression is observed among various inbred mouse strains

The primary and secondary responses to Tnp-Ficoll, a class 2 thymus-independent antigen, were assessed in various inbred strains of mice. The eventual implication of H-2 or IgH linked genes was searched for. Contrasting with our previous reports using Tnp-LPS, a class 1 thymus-independent antigen, no homologous memory-type response to Tnp-Ficoll and consequently no genetic control was observed. However Tnp-specific B-memory lymphocytes were induced in most strains since a heterologous challenge with Tnp-LPS evoked a typical memory type response characterized by an increased number of antibody-secreting cells and/or significant amount of anti-Tnp antibodies of the IgG isotype. The lack of memory revelation by Tnp-Ficoll is discussed in terms of a possible humoral or cellular regulation and of B-memory cell generation and maturation.     

The Hyperthermophilic Euryarchaeon Archaeoglobus fulgidus Repairs Uracil by Single-Nucleotide Replacement

Hydrolytic deamination of cytosine to uracil in cellular DNA is a major source of C-to-T transition mutations if uracil is not repaired by the DNA base excision repair (BER) pathway. Since deamination increases rapidly with temperature, hyperthermophiles, in particular, are expected to succumb to such damage. There has been only one report of crenarchaeotic BER showing strong similarities to that in most eukaryotes and bacteria for hyperthermophilic Archaea. Here we report a different type of BER performed by extract prepared from cells of the euryarchaeon Archaeoglobus fulgidus. Although immunodepletion showed that the monofunctional family 4 type of uracil-DNA glycosylase (UDG) is the principal and probably only UDG in this organism, a β-elimination mechanism rather than a hydrolytic mechanism is employed for incision of the abasic site following uracil removal. The resulting 3′ remnant is removed by efficient 3′-phosphodiesterase activity followed by single-nucleotide insertion and ligation. The finding that repair product formation is stimulated similarly by ATP and ADP in vitro raises the question of whether ADP is more important in vivo because of its higher heat stability.After depurination, hydrolytic deamination of cytosine to uracil is the most frequent event that damages DNA (36), and it results in G·C-to-A·T transition mutations if the damage is not repaired. In addition, some dUTP molecules escape hydrolysis by dUTPase, which results in a certain amount of dUMP introduced into DNA opposite adenine during replication (32). Irrespective of the mode of appearance, all cells contain uracil-DNA glycosylase (UDG) (EC 3.2.2.3) enzymes to remove uracil from DNA (17). The resulting abasic or apurinic/apyrimidinic (AP) site can subsequently be removed, and the integrity of the DNA can be restored by the so-called base excision repair (BER) pathway, which consists in its simplest form of the sequential actions of 5′-acting AP endonuclease, 5′-deoxyribose phosphate (dRP) lyase, DNA polymerase, and DNA ligase. The BER pathway can be initiated by one of several DNA glycosylases with different substrate specificities (17, 36, 57), and quantitatively it is the most important repair mechanism for the removal of spontaneously generated base modifications. Genes encoding bacterial and eukaryotic UDGs exhibiting significant selectivity for uracil have been cloned and sequenced in the last 2 decades, and the results have demonstrated that there is a high degree of conservation between distantly related species. Family 1 UDGs (for a review of UDG families 1 to 3, see reference 44), typified by the Escherichia coli Ung enzyme (37), recognize uracil in an extrahelical or flipped-out conformation in double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA). Several family 1 enzymes have been extensively characterized, both structurally and at the cell and organism levels. Family 2 UDGs, which includes E. coli Mug and mammalian thymine-DNA glycosylase, are mismatch specific and recognize guanine on the complementary strand rather than the lesion itself and thus are inactive with ssDNA. Family 3 UDGs, typified by the SMUG1 enzyme of human cells, have similar substrate requirements but exhibit a stronger preference for uracil in ssDNA than family 1 enzymes (17, 27, 57, 67).UDG activity in hyperthermophilic microorganisms was first reported in 1996 (33). Three years later, Sandigursky and Franklin (47) cloned and overexpressed an open reading frame (ORF) of the hyperthermophilic bacterium Thermotoga maritima that typifies the family 4 UDGs that are able to remove uracil from U·G and U·A base pairs, as well as from ssDNA. By means of homology searches, these workers found ORFs homologous to the T. maritima UDG gene in several prokaryotic genomes, including that of the hyperthermophilic archaeon Archaeoglobus fulgidus, a strict anaerobe that grows optimally at 83°C (60; for a review of DNA repair in hyperthermophilic archaea, see reference 20). Subsequently, they cloned and overexpressed the A. fulgidus ORF in E. coli by producing a His-tagged fusion protein. As expected, the purified A. fulgidus recombinant Afung (rAfung) protein exhibited UDG activity (48). However, whether Afung is the major UDG of A. fulgidus or is just a minor glycosylase with uracil-releasing ability remained to be determined.As a continuation of previous biochemical and physicochemical studies (31) of non-His-tagged rAfung protein, here we characterized a family 4 UDG in archaeon cell extract. The abundance of Afung in vivo was determined, and evidence indicates that this enzyme is the principal UDG of A. fulgidus. Here we also describe the mechanism of dUMP repair employed by this euryarchaeon, which differs in important ways from the mechanism reported for the crenarchaeon Pyrobaculum aerophilum (50).     

Isolation and characterization of rat kidney alanine aminopeptidase

Rat alanine aminopeptidase was purified from kidney by isolation of the brush border membrane with CaCl2 followed by differential centrifugation and tryptic proteolysis. It is a glycoprotein with a molecular weight of approximately 210,000 daltons comprising two 110,000-dalton subunits and has an amino acid composition similar to that of the human enzyme. Two zinc atoms are covalently bound to each protein subunit.