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Y Henry

Publications and source records attributed to Y Henry.

At least 55 records · Page 3Linked to original sources
PubMed1995

Inhibition of ribonucleotide reductase by nitric oxide derived from thionitrites: reversible modifications of both subunits.

Thionitrites are spontaneous nitric oxide (NO) donors in neutral aqueous solutions. Consequently, they inhibit ribonucleotide reductase, the rate-limiting enzyme in DNA synthesis, from Escherichia coli and murine adenocarcinoma TA3 cells. They also inhibit tumor cell proliferation. Reaction of thionitrites with protein R1, the large subunit, results in the nitrosation of cysteines, as shown from the formation of a chromophore with a characteristic absorption at 340 nm. EPR spectroscopy both on whole murine R2-overexpressing L1210 cells and on the pure protein showed that the tyrosyl radical of protein R2, the small subunit, reversibly couples to the NO radical, presumably leading to nitrosotyrosine adducts. Both molecular events might be at the origin of the inhibition of ribonucleotide reductase by NO, since a number of cysteines and the tyrosyl radical are essential for catalysis. These results identify NO donors as a new class of inhibitors of ribonucleotide reductase with potential applications as anticancer or antiviral chemotherapy agents.

Adenocarcinoma↗
PubMed1995

Foreign gene delivery into monocotyledonous species.

Monocotyledonous plants are generally more recalcitrant to genetic transformation than dicotyledonous species. The absence of reliable Agrobacterium-mediated transformation methods and the difficulties associated with the culture of monocotyledonous tissues in vitro are mainly responsible for this situation. Until recently, the genetic transformation of monocotyledons was essentially performed by direct transfer of DNA into regenerable protoplasts or intact cells cultured in vitro, via polyethylene glycol treatment, electroporation or particle bombardment. Since 1990, the use of particle gun technology has revolutionized the genetic engineering of monocotyledonous species, allowing transformation to be more independent of the in vitro culture requirements. Today, at least one genotype of each major monocotyledonous crop species, including cereals, can be genetically transformed.

Journal Article↗
PubMed1995

[Metalloproteins, cellular targets of nitric oxide: a concise review].

In this review we recall the main physical properties of nitric oxide. The irreversible reactions of NO with O2 and O2.-, which yield strongly oxydant and nitrosating, and therefore toxic, species, are described in kinetic terms. Nearly all metalloproteins are potential targets for NO, often detectable by EPR spectroscopy. The case of hemoglobin in vitro and within circulating erythrocytes, especially in pathophysiological cases, is particularly described. A few examples of hemoproteins activated or inhibited by NO are given. Results obtained with cellular systems responding to cytokines are summarized, together with the effects of NO synthesis on [FeS] clusters-containing proteins, on ribonucleotide reductase and on the proteins implicated in iron metabolism.

Animals↗
PubMed1994

Mutational analysis of an essential binding site for the U3 snoRNA in the 5' external transcribed spacer of yeast pre-rRNA.

The small nucleolar RNA U3 is essential for viability in yeast. We have previously shown that U3 can be cross-linked in vivo to the pre-rRNA in the 5' external transcribed spacer (ETS), at +470. This ETS region contains 10 nucleotides of perfect complementarity to U3. In a genetic background where the mutated rDNA is the only transcribed rDNA repeat, the deletion of the 10 nt complementary to U3 is lethal. Cells lacking the U3 complementary sequence in pre-rRNA fail to accumulate 18S rRNA: pre-rRNA processing is inhibited at sites A0 in the 5' ETS, A1 at the 5' end of 18S rRNA and A2 in ITS1. We show here that effects on processing at site A0 are specific for U3 and its associated proteins and are not seen on depletion of other snoRNP components. The deletion of the sequence complementary to U3 in the ETS therefore mimics all the known effects of the depletion of U3 in trans. This indicates that we have identified an essential U3 binding site on pre-rRNA, required in cis for the maturation of 18S rRNA.

Base Sequence↗
PubMed1994

Mutational analysis of an essential binding site for the U3 snoRNA in the 5' external transcribed spacer of yeast pre-rRNA.

The small nucleolar RNA U3 is essential for viability in yeast. We have previously shown that U3 can be cross-linked in vivo to the pre-rRNA in the 5' external transcribed spacer (ETS), at +470. This ETS region contains 10 nucleotides of perfect complementarity to U3. In a genetic background where the mutated rDNA is the only transcribed rDNA repeat, the deletion of the 10 nt complementary to U3 is lethal. Cells lacking the U3 complementary sequence in pre-rRNA fail to accumulate 18S rRNA: pre-rRNA processing is inhibited at sites A0 in the 5' ETS, A1 at the 5' end of 18S rRNA and A2 in ITS1. We show here that effects on processing at site A0 are specific for U3 and its associated proteins and are not seen on depletion of other snoRNP components. The deletion of the sequence complementary to U3 in the ETS therefore mimics all the known effects of the depletion of U3 in trans. This indicates that we have identified an essential U3 binding site on pre-rRNA, required in cis for the maturation of 18S rRNA.

Base Sequence↗
PubMed1994

Quenching of the tyrosyl free radical of ribonucleotide reductase by nitric oxide. Relationship to cytostasis induced in tumor cells by cytotoxic macrophages.

Nitric oxide (NO) synthesized by macrophages inhibits tumor cell replication. NO also inhibits ribonucleotide reductase, an enzyme essential for DNA synthesis, probably by quenching the catalytically active tyrosyl free radical of its R2 subunit. The role of this inhibition in NO-mediated cytostasis was thus evaluated. After a 4-h coculture with macrophages, quenching of the radical was demonstrated by electron paramagnetic resonance spectroscopy in transfected L1210-R2 cells over-expressing the R2 protein. Pronounced cytostasis was simultaneously observed. A NO synthase inhibitor greatly reduced both phenomena. Target cells withdrawn from macrophages partially recovered from cytostasis and radical loss within 90 min. Deoxyribonucleosides added to by-pass ribonucleotide reductase inhibition efficiently reversed cytostasis of K-562 cells. After a 24-h coculture, the quenched tyrosyl radical still reappeared in L1210-R2 cells withdrawn from macrophages, but DNA synthesis did not resume. Moreover, deoxyribonucleosides marginally reversed overnight cytostasis of K-562 cells mediated by macrophages but were efficient against cytostasis induced by hydroxyurea, a ribonucleotide reductase inhibitor. Autocrine cytostasis observed early in TA3-H2 cells committed to produce NO was closely correlated with quenching of the tyrosyl radical but not with formation of dinitrosyl-iron complexes. We thus propose that NO-dependent cytostasis begins with a rapid and reversible inhibition of ribonucleotide reductase, progressively reinforced by other, long-lasting antiproliferative effects.

Amino Acid Oxidoreductases↗
PubMed1994

The 5' end of yeast 5.8S rRNA is generated by exonucleases from an upstream cleavage site.

We have developed techniques for the detailed analysis of cis-acting sequences in the pre-rRNA of Saccharomyces cerevisiae and used these to study the processing of internal transcribed spacer 1 (ITS1) leading to the synthesis of 5.8S rRNA. As is the case for many eukaryotes, the 5' end of yeast 5.8S rRNA is heterogeneous; we designate the major, short form 5.8S(S), and the minor form (which is seven or eight nucleotides longer) 5.8S(L). These RNAs do not have a precursor/product relationship, but result from the use of alternative processing pathways. In the major pathway, a previously unidentified processing site in ITS1, designated A3, is cleaved. A 10 nucleotide deletion at site A3 strongly inhibits processing of A3 and the synthesis of 5.8S(S); processing is predominantly transferred to the alternative 5.8S(L) pathway. Site A3 lies 76 nucleotides 5' to the end of 5.8S(S), and acts as an entry site for 5'-->3' exonuclease digestion which generates the 5' end of 5.8S(S). This pathway is inhibited in strains mutant for XRN1p and RAT1p. Both of these proteins have been reported to have 5'-->3' exonuclease activity in vitro. Formation of 5.8S(L) is increased by mutations at A3 in cis or in RAT1p and XRN1p in trans, and is kinetically faster than 5.8S(S) synthesis.

Base Sequence↗
PubMed1994

Mitochondrial DNA variability detected in a single wheat regenerant involves a rare recombination event across a short repeat.

The mitochondrial genome of the selfed progeny of a plant regenerated from long-term somatic tissue culture displays specific structural rearrangements characterized by the appearance of novel restriction fragments. A mitochondrial DNA library was constructed from this selfed progeny in the SalI site of cosmid pHC79 and the novel fragments were subsequently studied. They were shown to arise from reciprocal recombination events involving DNA sequences present in the parental plant. The regions of recombination were sequenced and the nucleotide sequences were aligned with those of the presumptive parental fragments. We characterized an imperfect short repeated DNA sequence, 242 bp long, within which a 7-bp DNA repeat could act as a region of recombination. The use of PCR technology allowed us to show that these fragments were present in both parental plants and tissue cultures as low-abundance sequence arrangements.

Base Sequence↗
PubMed1994

[Nitric oxide: a biological effector. Detection using electron paramagnetic resonance].

Nitric oxide is synthesized in mammalian cells from L-arginine or from pharmaceutical drugs. It forms paramagnetic complexes with some metalloproteins, including hemoglobin. Induction of NOSi following LPS or cytokine activation of murine macrophages has various effects, such as inhibition of mitochondrial respiration and that of DNA biosynthesis through interaction of NO with specific metalloenzymes. Induction of NOSi in a generator cell such as macrophage gives the same metabolic effects in target cells. NO is also detected in pathological states such as septic shock, diabetes mellitus and allograft, where the inducible L-arginine-NO pathway plays an important role. Electron Paramagnetic Resonance spectroscopy enables to detect unambiguously such specific molecular targets for NO in mammalian whole cells and organelles.

Animals↗
PubMed1994

The addition of glutamic acid or protein to a threonine-deficient diet differentially affects growth performance and threonine dehydrogenase activity in fattening pigs.

The effects of dietary levels of threonine, protein (essential and nonessential amino acids) and glutamic acid (nonessential amino acid) on growth, food intake and threonine metabolism were studied in 54 fattening female pigs (Piétrain x Large White) from 40 to 100 kg live weight. Six experimental diets were compared using a 2 x 3 factorial design: two levels of threonine (0.42 and 0.52 g/100 g) corresponding to a limited and an adequate supply for growth, and three types of nitrogen supply: a basal diet supplying 12.6 g crude protein/100 g, a second diet providing additional protein to give a total supply of 15.6 g crude protein/100 g, and a third diet providing nonessential nitrogen in the form of L-glutamic acid to give the same total supply of 15.6 g crude protein/100 g diet. Protein addition to the basal diets did not modify growth performance but increased L-threonine-3-dehydrogenase (TDG) activity when pigs were fed the higher threonine diet. The addition of L-glutamic acid to the threonine-deficient diet improved growth performance, but there was no effect at the higher level of threonine. Glutamic acid increased TDG activity in pigs fed the low threonine diet. We conclude that glutamic acid may have a sparing effect on threonine when threonine is rate-limiting for protein deposition, but the mechanism of the interaction between the two amino acids remains unknown.

Alcohol Oxidoreductases↗
PubMed1993

Self-selection of lysine by growing pigs: choice combinations between deficient or suboptimal and adequate or superoptimal dietary levels according to sex.

Self-selection of dietary lysine was studied in one 42-d experiment involving 100 Large White growing pigs, with an equal number of females and castrated males, initially weighing 17.7 kg, within 5 treatments of 20 animals in each. A common basal diet (17% CP, 13.8 MJ DE/kg) based on maize, soybean meal and peanut meal, and containing a deficient level of lysine (0.61%), was used. Supplementary L-lysine was provided to obtain suboptimal (0.74%), optimal (0.85%) and superoptimal (1.21%) levels of total lysine for growth, as assumed from usual recommendations. In addition to treatment 1, a control where pigs were fed ad libitum a single diet with 0.85% lysine, 4 treatments with free choice of lysine within paired diets were compared. These included deficient or suboptimal levels of lysine on the one hand and optimal or superoptimal levels on the other according to a 2 x 2 factorial plan: 0.61 vs 0.85% (treatment 2), 0.74 vs 0.85% (treatment 3), 0.61 vs 1.21% (treatment 4), 0.74 vs 1.21% (treatment 5). The results showed sex difference in diet selection according to lysine content. Females had a distinct preference for the superoptimal level (1.21%) compared to the optimal level (0.85%), especially during the initial period of the trial, their requirement being higher than the presupposed 0.85% optimal level. For castrated males, the preference for lysine was restricted to the lower 0.85% level. The ability of females to self-select a greater proportion of the high lysine feed as opposed to castrated males was related to a higher potential for lean tissue growth. These results confirm that the growing pig is able to differentiate between diets differing only in their lysine contents. Complementary observations on plasma-free amino acids suggested the use of diets adequately balanced for amino acids when offered for free choice.

Amino Acids↗
PubMed1993

EPR characterization of molecular targets for NO in mammalian cells and organelles.

Nitric oxide is synthesized in mammalian cells from L-arginine or from pharmaceutical drugs. It forms paramagnetic complexes with some metalloproteins, inhibiting key enzymes in DNA synthesis, mitochondrial respiration, iron metabolism, etc. This article reviews how electron paramagnetic resonance spectroscopy helps to detect unambiguously such specific molecular targets for NO in mammalian whole cells and organelles. EPR has also been used for the detection of spin adducts of free NO by spin-trapping methods.

Animals↗
PubMed1992

Early loss of the tyrosyl radical in ribonucleotide reductase of adenocarcinoma cells producing nitric oxide.

Nitric oxide (NO) has been previously shown to inhibit crude preparations of ribonucleotide reductase, a key enzyme in DNA synthesis, and to destroy the essential tyrosyl free radical in pure recombinant R2 subunit of the enzyme. In R2-overexpressing TA3 cells, a decrease in the tyrosyl radical was observed by whole-cell EPR spectroscopy, as soon as 4 h after NO synthase induction by immunological stimuli. Complete loss of the tyrosyl EPR signal occurred after 7 h in cells cultured at a high density. Disappearance of the tyrosyl radical was prevented by N omega-nitro-L-arginine, a specific inhibitor of NO synthesis, and by oxyhemoglobin, which reacts rapidly with NO. It was reproduced by S-nitrosoglutathione, a NO-releasing molecule. Stable end products of NO synthase metabolism did not affect the radical. Immunoblot analysis of the R2 subunit indicated that expression of the protein was not influenced by NO synthase activity. These results establish that NO, or a labile product of NO synthase, induces the disappearance of the R2-centered tyrosyl radical. Since the radical is necessary for ribonucleotide reductase activity, its destruction by NO would contribute markedly to the antiproliferative action exerted by macrophage-type NO synthase.

Adenocarcinoma↗
PubMed1992

Cytochrome P450 catalyzes the oxidation of N omega-hydroxy-L-arginine by NADPH and O2 to nitric oxide and citrulline.

Rat liver microsomes catalyze the oxidative denitration of N omega-hydroxy-L-arginine (NOHA) by NADPH and O2 with formation of citrulline and nitrogen oxides like NO and NO2-. Besides NO2- and citrulline, whose simultaneous formation is linear for at least 20 min, the formation of NO could be detected under the form of its P450 and P420-Fe(II) complexes by UV-visible and EPR spectroscopy. Classical inhibitors of NO-synthases, like N omega-methyl-and N omega-nitro-arginine, fail to inhibit the microsomal oxidation of NOHA to citrulline and NO2-. On the contrary classical inhibitors of hepatic cytochromes P450 like CO, miconazole, dihydroergotamine and troleandomycin, strongly inhibit this monooxygenase reaction. These results show that the oxygenation of NOHA by NADPH and O2 with formation of citrulline and NO can be efficiently catalyzed by cytochromes P450 (with rates up to 1.5 turnovers per min for the cytochromes of the 3A subfamily).

Animals↗
PubMed1992

Formation of nitric oxide by cytochrome P450-catalyzed oxidation of aromatic amidoximes.

Rat liver microsomes catalyze the oxidation of para-hexyloxy-benzamidoxime 1 to the corresponding arylamide 2 and NO2-, by NADPH and O2. Involvement of cytochromes P450 as catalysts of this reaction was shown by the strong inhibitory effects of CO and miconazole and the spectacular increase of the activity upon treatment of rats with dexamethasone, a specific inducer of cytochromes P450 of the 3A subfamily. Formation of NO during oxidation of 1 was shown by detection of the formation of cytochrome P450- and cytochrome P420-Fe(II)-NO complexes by visible and EPR spectroscopy. The formation of these complexes should be responsible, at least in part, for the fast decrease of the rate of microsomal oxidation of 1 with time. These results suggest that exogenous compounds containing amidine or amidoxime functions could act as precursors of NO in vivo after in situ oxidation by cytochromes P450.

Animals↗
PubMed1992

Nuclear genes control changes in the organization of the mitochondrial genome in tissue cultures derived from immature embryos of wheat.

Although the mitochondrial genomes of the Chinese Spring and Aquila varieties of wheat are normally similar in organization, this is not so in tissue cultures initiated from their immature embryos where the mitochondrial genomes of both are rearranged and in different, characteristic, ways. However, the mitochondrial genomes of tissue cultures of reciprocal F1 crosses between these varieties were almost identical to one another, showing that nuclear genes control the rearrangement processes. These rearrangements are either due to the appearance of new structures or else result from changes in the relative amounts of subgenomic components. The severe reduction in the amount of certain molecular configurations in tissue cultures from reciprocal crosses is probably due to the presence of dominant information in the Aquila nuclear genome. Data obtained from tissue cultures initiated from F2 embryos of the cross Aquila x Chinese Spring suggest that at least two complementary genes are involved in this control. In contrast, the presence of new molecular arrangements appears to be under the control of a dominant allelic form of a Chinese Spring gene or genes. Thus, this study demonstrates that at least two sets of nuclear genes control the reorganization of the mitochondrial genome which occurs when tissue cultures are initiated from the immature embryos of wheat.

Blotting, Southern↗