[en] In ultraviolet-irradiated human fibroblasts inhibitors of DNA polymerases alpha (cytosine arabinoside, aphidicolin) and beta (dideoxythymidine) blocked polymerization of repair patches and accumulated large numbers of single-strand breaks in alkaline sucrose (up to 4-5 in 10₈ daltons). In nucleoid gradents, however, the restoration of DNA supercoiling to control levels after relaxation during excision repair was prevented only by aphidicolin, not be cytosine arabinoside or dideoxythymidine. These chain-terminating inhibitors must therefore generate breaks in DNA that are masked by proteins (possibly repair enzymes) that cannot be removed by the high-salt treatment of nucleoid gradients. Alkaline sucrose and nucleoid gradients therefore reveal different facets of the DNA breakage and rejoining during repair. The inhibitor of poly(ADP-ribose) synthesis, 3-aminobenzamide, had no effect on nucleoid sedimentation, implying that synthesis of this polymer plays no significant role in completion of repair of ultraviolet damage in human fibroblasts

[en] The unique ability of Carbon-13 nuclear magnetic resonance analysis with cross polarization/magic angle spinning techniques to investigate chemical structures of solids is used to probe the chemical characteristics of several gallstone types. New pulse program techniques are used to distinguish various carbon atoms in studying the polymeric nature of the black bilirubinoid pigment of pigment gallstones. Evidence for the involvement of the carboxyl group and noninvolvement of vinyl groups of bilirubinoids in the polymeric bond formation is presented. Conjugated bilirubin structures are found to be present in some solid residues from pigment stones extracted with acidic methanol/chloroform

[en] Using [³H]m⁷Gppp[¹⁴C]RNA-poly(A) from yeast as a substrate, an endoribonuclease has been detected in enzyme fractions derived from a high salt wash of ribonucleoprotein particles of Saccharomyces cerevisiae. The [³H]m⁷Gppp[¹⁴C]RNA-poly(A) seems to be a preferred substrate since other polyribonucleotides are hydrolyzed more slowly, if at all. The enzyme is inhibited by ethidium bromide, but fully double-stranded polyribonucleotides are not hydrolyzed. The hydrolysis of [³H]m⁷Gppp[¹⁴C]RNA-poly(A) is stimulated about 2.5-fold by the addition of small nuclear RNAs U1 and U2 of Novikoff hepatoma cells. Results show that the stimulation involves an interaction of the labeled RNA with the small nuclear RNA

[en] Using [³H]m₇Gppp[₁₄C]RNA-poly(A) from yeast as a substrate, an endoribonuclease has been detected in enzyme fractions derived from a high salt wash of ribonucleoprotein particles of Saccharomyces cerevisiae. The [₃H]m₇Gppp[₁₄C]RNA-poly(A) seems to be a preferred substrate since other polyribonucleotides are hydrolyzed more slowly, if at all. The enzyme is inhibited by ethidium bromide, but fully double-stranded polyribonucleotides are not hydrolyzed. The hydrolysis of [₃H]m₇Gppp[₁₄C]RNA-poly(A) is stimulated about 2.5-fold by the addition of small nuclear RNAs U1 and U2 of Novikoff hepatoma cells. Results show that the stimulation involves an interaction of the labeled RNA with the small nuclear RNA

[en] In rat hippocampal slices, carbachol and norepinephrine induce an accumulaton of [³H]-inositol-1-phosphate which is markedly amplified in the presence of lithium. The tumor-promoting agents phorbol 12, dilat 13 dibutyrate (PDB) and 4β phorbol, 12β-myristate, 13 α-acetate (PMA) have no effect on [³H] inositol-1-phophate accumulation alone, but when preincubated with hippocampal slices significantly inhibit the accumulation of [³H]-inositol-1-phosphate induced by carbachol and norepinephrine. The IC₅₀ values of PDB and PMA are 0.2 μM and 25μM respectively. In contrast, the weak tumor promoting agents 4-O-methylphorbol 12 myristate 13 acetate (MPMA) and phorbol 13,20-diacetate (P 13,20 DA) only slightly attenuate the agonist-induced response at concentrations less than or equal to100μM, whereas 4α-phorbol (4α-PHR), a biologically inactive phorbol, has no effect. These data suggest that phorbol ester receptor-mediated events may be negatively coupled to agonist-induced phosphatidylinositol hydrolysis. 17 references, 3 figures

[en] The extent of the deficiency in γ-ray induced DNA repair synthesis in an ataxia telangiectasia (AT) human fibroblast strain was found to show no oxygen enhancement, consistent with a defect in the repair of base damage. Repair deficiency, but not repair proficiency, in AT cells was accompanied by a lack of inhibition of DNA synthesis by either γ-rays or the radiomimetic drug bleomycin. Experiments with 4-nitroquinoline 1-oxide indicated that lack of inhibition was specific for radiogenic-type damage. Thus excision repair, perhaps by DNA strand incision or chromatin modification, appears to halt replicon initiation in irradiated repair proficient cells whereas in repair defective AT strains this putatively important biological function is inoperative

[en] The metabolic pathway for 1-alkyl-2-acetyl-sn-glycerols, a recently discovered biologically active neutral lipid class, was elucidated in experiments conducted with rabbit platelets. The total lipid extract obtained from platelets incubated with 1-[1-,2-³H]alkyl-2-acetyl-sn-glycerols or 1-alkyl-2-[³H]acetyl-sn-glycerols contained at least six metabolic products. The six metabolites, identified on the basis of chemical and enzymatic reactions combined with thin-layer or high-performance liquid chromatographic analyses, corresponded to 1-alkyl-sn-glycerols, 1-alkyl-2-acetyl-sn-glycero-3-phosphates, 1-alkyl-2-acyl(long-chain)-sn-glycero-3-phosphoethanolamines, 1-alkyl-2-acetyl-sn-glycero-3-phosphoethanolamines, 1-alkyl-2-acyl(long-chain)-sn-glycero-3-phosphocholines, and 1-alkyl-2-actyl-sn-glycero-3-phosphocholines (platelet activating factor). These results indicate that the metabolic pathway for alkylacetylglycerols involves reaction steps catalyzed by the following enzymatic activities: choline- and ethanolamine- phosphotransferases, acetyl-hydrolase, an acyltransferase, and a phosphotransferase. The step responsible for the biosynthesis of platelet activating factor would appear to be the most important reaction in this pathway and this product could explain the hypotensive activities previously described for alkylacetyl-(or propionyl)-glycerols. Of particular interest was the preference exhibited for the utilization of the 1-hexadecyl-2-acetyl-sn-glycerol species in the formation of platelet activating factor

[en] Alterations in the synthesis of proteins following exposure of Saccharomyces cerevisiae to UV light were investigated using radioactive labelling and two dimensional electrophoresis. UV-irradiation induced the synthesis of various proteins. Among them the analogue of the RecA protein of Escherichia coli (Angulo et al. 1985) and two other polypeptides (34 Kd and 35 Kd, pI 5.8) were observed in all four strains analyzed namely two DNA-repair deficient (rad−) strains : (rad6-1 and pso2-1) and their isogenic wild type RAD+ strains

[en] Nitrite reductase as isolated from Desulfovibrio desulfuricans shows a complex set of rhombically distorted high-spin ferric heme and low-spin ferric heme resonances at 11⁰K. These resonances disappear on enzymatic reduction with hydrogen, hydrogenase from D. vulgaris and FAD as redox mediator. The addition of nitrite to the reduced enzyme results in reoxidation of nitrite reductase as evidenced by the reappearance of most of the initial signal intensities of high-spin and low-spin ferric heme resonances. Simultaneously an intense and unusual broadened signal appears in the g = 2 region, suggesting the formation of a novel heme-nitric oxide signal with the main g-value at 2.08. Confirmation of this heme-nitric oxide complex was demonstrated by reoxidation of reduced enzyme with ¹⁵NO₂^-1 instead of ¹⁴NO₂^-1 resulting in a decrease from three to two of the hyperfine interaction pattern of nitrogen. Thus nitrite reduction to ammonia by nitrite reductase occurs via a heme-nitric oxide intermediate as reported with spinach nitrite reductase

[en] Resonance Raman investigations of the Fe-O₂ stretching frequency in oxyhemoglobin containing isotopically unsymmetric ¹⁶O-¹⁸O point to an end-on geometry, rather than a side-on one