Inhibition of iron uptake in HL60 cells by 2-formylpyridine monothiosemicarbazonato Cu(II).

The electron paramagnetic resonance (EPR) signal of the tyrosyl radical attributed to ribonucleoside diphosphate reductase decreases after treatment of promyelocytic leukemic HL60 cells with 2-formylpyridine thiosemicarbazonato copper(II) (CuL). According to EPR studies, CuL forms adducts with both histidine and cysteine-like Lewis bases associated with isolated membranes from HL60 cells. After the addition of CuL, the EPR signal for the cysteine-like adduct decreases substantially over a 15-min period. The reduction of signal is consistent with oxidation of thiols as shown by an analysis of sulfhydryl content. It is hypothesized that receptor-mediated transferrin internalization is inhibited by oxidation of critical thiols. Since the uptake of 59Fe-transferrin is greatly inhibited by the treatment of HL60 cells with CuL, the reduced uptake of iron by cells, in the presence of CuL, may lead to decreased iron availability for the activity of the M2 subunit of ribonucleotide reductase and a subsequent decrease in the tyrosyl radical signal of the enzyme. Moreover, the intact subunit M2 is no longer detected by EPR, even after the addition of excess iron.     

3-Hydroxy-3-methylglutaryl coenzyme A lyase: affinity labeling of the Pseudomonas mevalonii enzyme and assignment of cysteine-237 to the active site.

Pseudomonas mevalonii 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) lyase is irreversibly inactivated by the reactive substrate analog 2-butynoyl-CoA. Enzyme inactivation, which follows pseudo-first-order kinetics, is saturable with a KI = 65 microM and a limiting k(inact) of 0.073 min-1 at 23 degrees C, pH 7.2. Protection against inactivation is afforded by the competitive inhibitor 3-hydroxyglutaryl-CoA. Labeling of the bacterial enzyme with [1-14C]-2-butynoyl-CoA demonstrates that inactivation coincides with covalent incorporation of inhibitor, with an observed stoichiometry of modification of 0.65 per site. Avian HMG-CoA lyase is also irreversibly inactivated by 2-butynoyl-CoA with a stoichiometry of modification of 0.9 per site. Incubation of 2-butynoyl-CoA with mercaptans such as dithiothreitol results in the formation of a UV absorbance peak at 310 nm. Enzyme inactivation is also accompanied by the development of a UV absorbance peak at 310 nm indicating that 2-butynoyl-CoA modifies a cysteine residue in HMG-CoA lyase. Tryptic digestion and reverse-phase HPLC of the affinity-labeled protein reveal a single radiolabeled peptide. Isolation and sequence analysis of this peptide and a smaller chymotryptic peptide indicate that the radiolabeled residue is contained within the sequence GGXPY. Mapping of this peptide within the cDNA-deduced sequence of P. mevalonii HMG-CoA lyase [Anderson, D. H., & Rodwell, V. W. (1989) J. Bacteriol. 171, 6468-6472] confirms that a cysteine at position 237 is the site of modification. These data represent the first identification of an active-site residue in HMG-CoA lyase.     

Gap junctions in myometrial cell cultures: evidence for modulation by cyclic adenosine 3':5'-monophosphate.

Primary cultures of myometrial cells from juvenile rats, continuous cultures maintained by serial passage, and a pSV3neotransfected myometrial cell line were established and utilized for the study of development and modulation of gap junctional intercellular communication (GJIC) in vitro. The smooth muscle origin and homogeneity of the cultures were verified by immunofluorescence staining of alpha-smooth muscle actin and cellular desmin. Although gap junctions were not detected in thin sections of juvenile and adult myometrial tissues by transmission electron microscopy, they were detected in cultured myometrial cells derived from juvenile and adult animals. The presence of GJIC in cultured cells was confirmed using a fluorescence recovery after photo-bleaching assay. Administration of exogenous estradiol-17 beta (10(-7) M) resulted in an increase in GJIC in primary and passage 9 myometrial cultures, whereas pSV3neo-transfected myometrial cells were not significantly different from untreated controls. The lack of estrogen responsiveness in pSV3neo-transfected cultures correlated with lower levels of estrogen receptors than in primary cultures. Addition of 1 mM 8-bromo-cAMP resulted in rapid (within 2 min) increases in dye transfer in both control and estradiol-17 beta-primed primary cultures. Uncoupling of cells by treatment with 1 mM 1-octanol, followed by addition of 1 mM 8-bromo-cAMP, resulted in increased GJIC in control and estradiol-17 beta-primed cultures, although up-regulation of GJIC in estradiol-17 beta-primed cultures was much greater than in control cultures. Comparative experiments carried out on a spontaneously immortalized rat granulosa cell line (SIGC), which expresses the same connexin43 species as myometrial cells, exhibited similar responses to exogenous 8-bromo-cAMP following uncoupling of gap junctions with octanol. While the results of these investigations may not be extrapolated to myometrium in vivo, they suggest that myometrial cell culture may offer additional opportunities to explore the temporal expression and modulation of GJIC in myometrium.     

Characterization of a toxin fromParthenium hysterophorus and its mode of excretion in animals

Fractionation of methanolic extracts of air dried aerial parts ofParthenium resulted in the isolation of a toxic constituent which was identified as parthenin, the major sesquiterpene lactone from the weed. The LD₅₀ (minimal lethal dose required to cause 50% mortality) for parthenin in rats was 42 mg/kg body weight. When [³H]-parthenin was given orally or by intravenous administration, radioactivity appeared in the milk of lactating laboratory and dairy animals. Tissue distribution of radioactivity revealed that maximum label was detectable in kidneys.     

Control of glycoprotein synthesis. UDP-GlcNAc:glycopeptide beta 4-N-acetylglucosaminyltransferase III, an enzyme in hen oviduct which adds GlcNAc in beta 1-4 linkage to the beta-linked mannose of the trimannosyl core of N-glycosyl oligosaccharides

Hen oviduct membranes are shown to catalyze the following enzyme reaction: GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-2Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-6)GlcNAc-Asn + UDP-GlcNAc leads to GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-2Man alpha 1-3)GlcNAc beta 1-4)Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-6)GlcNAc-Asn + UDP. The enzyme catalyzing this reaction has been named UDP-GlcNAc:glycopeptide beta 4-N-acetylglucosaminyltransferase III (GlcNAc-transferase III) to distinguish it from two other GlcNAc-transferases (I and II) present in hen oviduct and previously described in several mammalian tissues. GlcNAc-transferases I and II, respectively, attach GlcNAc in beta 1-2 linkage to the Man alpha 1-3 and Man alpha 1-6 arms of Asn-linked oligosaccharide cores. A specific assay for GlcNAc-transferase III was devised by using concanavalin A/Sepharose columns to separate the product of transferase III from other interfering radioactive glycopeptides formed in the reaction. The specific activity of GlcNAc-transferase III in hen oviduct membranes is about 5 nmol/mg of protein/h. Substrate specificity studies have shown that GlcNAc-transferase III requires both terminal beta 1-2-linked GlcNAc residues in its substrate for maximal activity. Removal of the GlcNAc residue on the Man alpha 1-6 arm reduces activity by at least 85% and removal of both GlcNAc residues reduces activity by at least 93%. Two large scale preparations of product were subjected to high resolution proton NMR spectroscopy to establish the incorporation by the enzyme of a GlcNAc in beta 1-4 linkage to the beta-linked Man. This GlcNAc residue is called a "bisecting" GlcNAc and appears to play important control functions in the synthesis of complex N-glycosyl oligosaccharides. Several enzymes in the biosynthetic scheme are unable to act on glycopeptide substrates containing a bisecting GlcNAc residue.     

Osmotin gene expression is controlled by elicitor synergism

Arachidonic acid (AA), a fatty-acid fungal elicitor, and a cellulase preparation from Aspergillus niger , a protein-type fungal elicitor, induced osmotin gene expression. Both elicitors activated the osmotin promoter fused to a β-glucuronidase (GUS) reporter gene in a tissue-specific manner in tobacco seedlings ( Nicotiana tabacum L. cv. Wisconsin 38). The cellulase preparation was more effective than AA at the concentrations tested and, unlike AA, also induced the accumulation of osmotin mRNA and protein. Combinations of AA and the cellulase preparation had a greater than additive effect on the activation of the osmotin promoter and the accumulation of osmotin mRNA and protein. Both AA and the cellulase preparation, when applied separately, were virtually ineffective in the induction of the osmotin promoter in cotyledon tissues. However, together they were able to induce synergistically GUS fused to the osmotin promoter. Increases in osmotin-promoter-driven GUS activity and accumulation of osmotin mRNA induced by AA, the cellulase preparation or their combination were reversed by norbornadiene, an ethylene action inhibitor, indicating that ethylene is involved in the induction of the osmotin gene by these elicitors.     

Comparative study of the glycosphingolipids of chicken bursa of Fabricius and of chicken, rat and human thymus.

1. The glycosphingolipid compositions of the thymus and bursa of Fabricius of young male chickens were compared. The two tissues were found to contain complex mixtures of both neutral glycosphingolipids and gangliosides. Both tissues contained mono-, di-, tri-, tetra- and penta-glycosylceramides; the pentaglycosylceramide displayed a reaction of identity with authentic Forssman antigen when tested against a specific anti-(Forssman antigen) serum. The ganglioside G(m3) containing N-acetylneuraminic acid was the principle ganglioside of both tissues. 2. The thymus contained appreciable amounts of the simple ganglioside N-acetylneuraminylgalactosylceramide, a compound not found in the bursa. The ganglioside G(d3) (disialohaematoside) was detected in both tissues. 3. Rat and human thymus, like sheep thymus (Narasimhan, Hay, Greaves & Murray (1976) Biochim, Biophys. Acta 431, 578-591), both contained a tetraglycosylceramide species as their most complex neutral glycosphingolipid and possessed little or no Forssman antigen. They also contained a complex mixture of gangliosides. 4. The possible significance of these results is briefly discussed.