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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The structure of polyguanylic acid (poly G) at neutral pH has been studied by optical and calorimetrical methods. It can be shown that diverging from earlier findings Poly G reversibly undergoes a cooperative thermal transition. Thermal denaturation curves are recorded at 253 nm as a function of the sodium ion concentration. The denaturation enthalpy of poly G in dilute aqueous solution is determined to 2.2 kcal/mole g. It is concluded, that the part of the ordered poly G structure, which gives rise to a temperature dependent cooperative transition, arises from stacking interactions of adjacent bases in the single strand.
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PMID:A calorimetric study of polyguanylic acid at neutral pH. 1 20

Very complex glycosphingolipids with A, H and I blood-group activities were isolated from human erythrocyte membranes. The membranes were obtained from erythrocytes of blood group A, A2 and O respectively. A general formula for the antigens is: (Fuc)3-4(Gal)n(LlcNAc)n-2(Glc)1(Sphingosine)1(where Fus is fucose, Gal is galactose, GlcNAc is N-acetylglucosamine and Glc is glucose) with values of n ranging from 10-27. A-active preparations contain additionally 2-3 residues of N-acetylgalactosamine. In view of the unusual complexity of these compounds they were designated poly(glycosyl)ceramides (formerly megaloglycolipids). Individual poly(glycosyl)ceramide fractions were isolated from A erythrocytes and were found to differ by about 8 glycosyl residues per molecule forming a series of compounds with 22, 30, 38, 51 and 59 glycosyl residues per mole. Structural studies indicate that the main sequence of poly(glycosyl)ceramides consists of the residues of galactopyranose and 2-deoxy-2-acetamidoglucopyranose substituted at 3 and 4 position respectively. These residues are probably alternating. N-Acdtylglucosamine substituted at 3 position was not found in poly(glycosyl)ceramides. Brances of poly(glycosyl)ceramides originate from 3 and 6 position of galactopyranosyl residues. The number of branches is proportional to the degree of molecular complexity. In poly(glycosyl)ceramides isolated from A and A2 erythrocytes the branches are terminated with the following structures GalNAc alpha 1 leads to 3 [Fuc alpha 1 leads to 2] Gal; Fuc alpha 1 leads to 2 Gal and Gal (presumably Gal beta 1 leads to 4 GlcNAc). In poly(glycosyl)ceramides from A cells the total number of A and H-active structures per average molecule of 30-35 glycosyl residues amounts to 2.1 and 1.2 respectively while the number of terminal galactose structures is 1.8. For poly(glycosyl)ceramides from A2 erythrocytes the corresponding figures are 0.75, 3.5, and 2.1 respectively. Poly(glycosyl)ceramides from O cells comprise about 3.8 H-active structures and 1.8 terminal galactopyranosyl residues. In poly(glycosyl)ceramides with high "n" values the number of terminal galactose structures is increased. These fractions display high blood-group I activity. However, the removal of terminal galactose with beta-galactosidase affects I-activity only slightly.
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PMID:Isolation and characterization of poly(glycosyl)ceramides (megaloglycolipids) with A, H and I blood-group activities. 82 47

In an attempt to improve bifunctional chelate labelling of Mab, we investigated the use of a polyamino acid backbone for multiple DTPA substitutions. Poly-L-lysine (PL) (3.8 Kd, n = 25) was partially acetylated with MADTPA to yield 11 moles of DPTA per mole of PL. The average numbers of DTPA on PL were directly quantified with MADTPA-C-14. The remaining epsilon amino groups on PL-DTPA (I) were measured with TNBS reagent. A selective maleimide derivatization of (I) with S-SMPB yielded (II), which contains 2.3 moles of maleimide groups per mole of (I). The sulfhydryl activation of Mab-TP41.2F(ab')2 with 2-Iminothiolane hydrochloride produced (III), containing 1.3 moles of sulfhydryl groups per mole of Mab. Compounds (II) and (III) were combined to form a single thioether-spaced chain linkage of Mab-PL-DTPA (IV), which was subsequently chelated with 111In to yield (V), which was the compound of interest. Indium-111-PL-DTPA (VI) and 111In-DTPA-MabTP41.2F(ab')2 (VII) also were prepared for control studies. Direct cell binding assay revealed the mean immunoreactivity of (V) to be 79.4% and that of (VII) to be 39.5%. In a biodistribution study on melanoma tumor-bearing athymic mice at 4, 24, and 48 hr postinjection, the tumor/blood and tumor/liver ratios at 48 hr were 11.6 and 1.2 for (V), compared to 3.7 and 0.13, respectively, with (VII). Thus, the PL configuration for radiolabeled antibodies seems to result in decreased hepatic accumulation and retained tumor activity. The findings suggest that further studies of this new compound are warranted.
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PMID:Reduced hepatic accumulation of radiolabeled monoclonal antibodies with indium-111-thioether-poly-L-lysine-DTPA-monoclonal antibody-TP41.2F(ab')2. 155 42

A series of copolymers of glycine and DL-lactic acid with various compositions was synthesized and their in vivo and in vitro degradation behavior was studied. For the in vivo examination, discs of the copolymer films were subcutaneously implanted in rats. The in vitro studies were carried out in phosphate buffer at pH = 7.4 and 37 degrees C. The decrease in molecular weight, the loss of weight, and the tissue reactions of the different copolymers were determined after 2, 5, and 10 weeks. Poly(DL-lactic acid) was used as reference material. The in vivo and in vitro degradation behavior of the polymers was comparable. The decrease of molecular weight of the copolymers and poly(DL-lactic acid) in time was similar. The weight loss for copolymers with a higher mole fraction of glycine units started earlier. The copolymer with the highest content of glycine units disappeared completely within 10 weeks both in vivo and in vitro. The poly(DL-lactic acid) implant lost only 25% weight over the same period. Tissue reactions against all materials started with an acute inflammatory reaction caused by the trauma of implantation, followed by wound-healing processes, ending in a very mild foreign body reaction for the poly(DL-lactic acid) and a more excessive macrophage mediated foreign body reaction for the glycine/DL-lactic acid copolymers. The tissue reaction was more severe for polymers having a higher rate of degradation.
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PMID:In vivo and in vitro degradation of glycine/DL-lactic acid copolymers. 260 21

The purpose of these experiments was to obtain proinsulin mRNA from catfish pancreatic islets and synthesize its cDNA. Poly(A)-rich mRNA was electrophoresed on preparative agarose-urea gels. One RNA fraction was obtained which translated predominantly preproinsulin. This mRNA was estimated to be approx. 210 000 Mr (650 nucleotides) when electrophoresed under denaturing conditions. [3H]Proinsulin cDNA was hybridized to excess RNA to monitor purification of mRNA from total islet RNA. Greater than 94% of proinsulin messenger contained poly(A) sequences. [3H]Proinsulin cDNA hybridized to its template mRNA with a Rot 1/2 of 4.4 x 10(-3) mole x sec/l. The overall purification was 80-fold by this type of analysis. Thermal denaturation studies indicated a high degree of fidelity of hybrid formation between [3H]proinsulin cDNA and proinsulin mRNA. Proinsulin comprised 20% of total islet protein when synthesis was measured in vivo (Albert and Permutt, 1979) and 12-20% when total islet mRNA was translated in a cell-free system. Using the [3H]proinsulin cDNA probe it was estimated that proinsulin mRNA accounted for approx. 15% of total islet mRNA.
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PMID:Isolation of catfish proinsulin messenger RNA and synthesis of its complementary DNA. 615 87

Poly[d(A-T)].poly[d(A-T)], when reconstituted with chicken erythrocyte core histones and subsequently incubated with sufficient histone H5 in a solution containing polyglutamic acid, forms structures resembling chromatin. H5 induces nucleosome alignment in about two hours at physiological ionic strength and 37 degrees C. The nucleosome spacing and apparent linker heterogeneity in the assembled nucleoprotein are very similar to those in chicken erythrocyte chromatin. Also, condensed chromatin-like fibers on the polynucleotide can be visualized. The binding of one mole of H5 per mole of core octamer is necessary to generate the physiological nucleosome spacing, which remains constant with the addition of more H5. The nucleosome repeat length is not a function of the core histone to poly[d(A-T)] ratio for values lower than the physiological ratio. With increasing ratios, in excess of the physiological value, nucleosome spacing first becomes non-uniform, and then takes on the close packing limit of approximately 165 base-pairs. In addition to eliminating possible base sequence effects on nucleosome positioning, poly[d(A-T)] allows nucleosomes to slide more readily than does DNA, thereby facilitating alignment. Evidence is presented that polyglutamic acid facilitates the nucleosome spacing activity of histone H5, primarily by keeping the nucleoprotein soluble. This model system should be useful for understanding how different repeat lengths arise in chromatin.
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PMID:A model chromatin assembly system. Factors affecting nucleosome spacing. 620 68

Poly(His-Asp-Ser-Gly) was synthesized from the fully protected tetrapeptide active ester hydrochloride, which was prepared by stepwise coupling, using pentachlorophenyl ester and mixed anhydride methods. Complete deprotection of the protected tetrapeptide polymer was achieved by using 90% trifluoroacetic acid. The free polymer was dialyzed for 24 hr using a membrane (which retains molecules with molecular weights greater than 5000). The catalytic activity was determined by studying the hydrolysis of p-nitrophenyl acetate in 0.2 M phosphate buffer (pH 7.4) at 37 degrees. The catalytic coefficient of the dialyzed polymer was found to be 138 liters/mole/min.
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PMID:Synthesis and catalytic activity of poly-L-histidyl-L-aspartyl-L-seryl-glycine. 715 87

The occurrence of alternative structures for the lithium, sodium, and potassium salts of poly(dG-dC) was determined as a function of hydration using IR spectra of nonoriented gels. Poly(dG-dC).K with added KCl (r = 0.56 where r is the moles of KCl per mole of nucleotide residue) gave results essentially identical to the much studied poly(dG-dC).Na with added NaCl (r = 0.56). Both gave a sharp transition from a unique B structure (hereafter designated B*) to the Z structure upon dehydration. Poly(dG-dC).Li with added LiCl (r = 0.36) assumed the B* structure at high hydration but made a broad transition to the C structures as hydration was lowered. We believe this is the first clear evidence of the C structure for poly(dG-dC). No other structures (A, D, or Z) were observed at any hydration in nonoriented gels. Poly(dG-dC).Na with added ZnCl2 (r = 0.2) existed as a mixture of the B* and Z structures in maximally hydrated gels. A broad, incomplete transition to a higher mole fraction of Z structure occurred upon dehydration. Zn2+ promotes the Z structure for poly(dG-dC) and appears to bind to guanine residues. Poly(dG-dC).Na with added MgCl2 or CaCl2 (r = 0.2) assumed the normal B* structure at maximum hydration with no hint of Z structure. Slight dehydration produced a very sharp transition to the Z structure. Both Mg2+ and Ca2+ are strong promoters of the Z structure but do not bind to cytosine or guanine residues.
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PMID:Conditions for the stability of the B, C, and Z structural forms of poly(dG-dC) in the presence of lithium, potassium, magnesium, calcium, and zinc cations. 847 15

Infrared spectra were used to show that the sodium salts of acetate, sulfate and phosphate (pH 7.2) selectively stabilize some of the alternative structures of poly(dG-dC).Na and poly(dA-dT).Na as a function of hydration in nonoriented gels. NaCl was used as a reference. Each anion was present at 0.36 mole per mole of nucleotide residue. The weak absorption bands from these anions did not interfere with conclusive interpretation of the IR spectra of the polynucleotides. Poly(dG-dC).Na assumed the usual B* structure with each of the anions at high hydrations (r.h. of the ambient air > or = 94%). Lowering the hydration gave the following results. With acetate, the B* structure remained with only a small fraction of a modified Z or some other unusual structure present. With sulfate or phosphate, a sharp transition to the Z structure occurred (essentially complete by 86% r.h.). With reference to chloride ions, acetate favors the B* while sulfate and phosphate (pH 7.2) favors the Z structure. Poly(dA-dT).Na assumed the usual B structure with each of the anions at high hydrations. Lowering the hydration gave the following results. With acetate, the A structure was observed at the same hydrations as with chloride. With sulfate, a sharper transition to the A structure occurred (complete by 80% r.h.). With phosphate, a still sharper transition to the A structure occurred (complete by 86% r.h.). With reference to chloride, acetate shows little difference but sulfate and phosphate (pH 7.2) promote the A over the B structure. These results are compared with past results for NaNO3.
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PMID:Structures of poly(dG-dC) and poly(dA-dT) stabilized by anions. 852 31

Formamide lowers melting temperatures (Tm) of DNAs linearly by 2.4-2.9 degrees C/mole of formamide (C(F)) depending on the (G+C) composition, helix conformation and state of hydration. The inherent cooperativity of melting is unaffected by the denaturant. dTm/dC(F)for 11 plasmid domains of 0.23 < (G+C)<0.71 generally fit to a linear dependence on (G+C)-content, which, however, is consistent with a (G+C)-independent alteration in the apparent equilibrium constant for thermally induced helix <--> coil transitions. Results indicate that formamide has a destabilizing effect on the helical state, and that sequence-dependent variations in hydration patterns are primarily responsible for small variations in sensitivity to the denaturant. The average unit transition enthalpy delta H(m)[see text for complete expression], exhibits a biphasic dependence on formamide concentration. The initial drop of -0.8 kcal/mol bp at low formamide concentrations is attributable to a delta delta H(m)[see text for complete expression], for exchange of solvent in the vicinity of the helix: displacement by formamide of weakly bound hydrate or counterion. The phenomenological effects are equivalent to lowering the bulk counterion concentration. Poly(dA.dT) exhibits a much lower sensitivity to formamide, due to the specific pattern of tightly bound, immobilized water bridges that buttress the helix from within the narrow minor groove. Tracts of three (A.T)-pairs behave normally, but tracts of six exhibit the same level of reduced sensitivity as the polymer, suggesting a conformational shift as tracts are elongated beyond some critical length [McCarthy J.G. and Rich,A. (1991) Nucleic Acids Res. 19, 3421-3429].
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PMID:Thermodynamic effects of formamide on DNA stability. 866 41


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