(1/139) Regulation of de novo purine biosynthesis in human lymphoblasts. Coordinate control of proximal (rate-determining) steps and the inosinic acid branch point.

Purine nucleotide synthesis de novo has been studied in a permanent tissue culture line of human splenic lymphoblasts with particular attention to coordination of control of the proximal (rate-determining) steps with the distal branch point of the pathway. An assay was used which permits simultaneous determination of the overall rate of labeling of all intracellular purines with sodium [14C]formate, as well as the distribution of isotope into all intracellular guanine- and adenine-containing compounds. The guanine to adenine labeling ratio was used as an index of IMP branch point regulation. It was found that exogenous adenine and guanine produce feedback-controlling effects not only on the first step in the de novo pathway, but also on the IMP branch point. Concentrations of adenine which produce less than 40% inhibition of the overall rate of de novo purine synthesis do so by selectively inhibiting adenine nucleotide synthesis de novo by 50 to 70% while stimulating guanine nucleotide synthesis de novo by up to 20%. A reciprocal effect is seen with exogenous guanine. The adenosine analog 6-methylmercaptopurine ribonucleoside selectivity inhibits adenine nucleotide synthesis via the de novo pathway but not from exogenous hypoxanthine. Thus, the reactions of purine nucleotide interconversion, in particular adenylosuccinate synthetase, may be regulated differently in cells deriving their purine nucleotides solely from de novo synthesis than when deriving them via "salvage" of preformed hypoxanthine.  (+info)

(2/139) Effect of 9-beta-D-arabinofuranosyladenine 5'-monophosphate and 9-beta-D-arabinofuranosylhypoxanthine 5'-monophosphate on experimental herpes simplex keratitis.

Treatment of established experimental keratitis caused by herpes simplex virus with 9-beta-d-arabinofuranosyladenine 5'-monophosphate (Ara-AMP) or 9-beta-d-arabinofuranosylhypoxanthine 5'-monophosphate (Ara-HxMP) showed that the Ara-AMP, in a concentration of 2 or 20%, had a significant effect on the keratitis but that 0.4% Ara-HxMP showed only minimal activity. Ara-AMP was also effective in the treatment of idoxuridine-resistant keratitis. No local toxicity with a high concentration (20%) of Ara-AMP was seen, but the duration of therapy was brief.  (+info)

(3/139) Synthetic study on carbocyclic analogs of cyclic ADP-ribose, a novel second messenger: an efficient synthesis of cyclic IDP-carbocyclic-ribose.

An efficient synthesis of cyclic IDP-carbocyclic-ribose, as a stable mimic for cyclic ADP-ribose, was achieved. 8-Bromo-N1-carbocyclic-ribosylinosine derivative 10, prepared from N1-(2,4-dinitrophenyl)inosine derivative 5 and an optically active carbocyclic amine 6, was converted to 8-bromo-N1-carbocyclic-ribosylinosine bisphosphate derivative 15. Treatment of 15 with I2 in the presence of molecular sieves in pyridine gave the desired cyclic product 16 quantitatively, which was deprotected and reductively debrominated to give the target cyclic IDP-carbocyclic-ribose (3).  (+info)

(4/139) Stability of disodium salt of inosine phosphate in aqueous solutions.

The HPLC method for the separation of the disodium salt of inosine phosphate (PIN) and the product of its transformation, inosine (IN) and hypoxanthine (HP) were developed and validated. The hydrolysis kinetics of disodium salt of inosine phosphate was studied in aqueous solution at 353 K over a pH range of 0.45-12.13.  (+info)

(5/139) Brush border motility. Microvillar contraction in triton-treated brush borders isolated from intestinal epithelium.

The brush border of intestinal epithelial cells consists of an array of tightly packed microvilli. Within each microvillus is a bundle of 20-30 actin filaments. The basal ends of the filament bundles are embedded in and interconected by a filamentous meshwork, the terminal web, which lies directly beneath the microvilli. When calcium and ATP are added to isolated brush borders that have been treated with the detergent, Triton X-100, the microvillar filament bundles rapidly retract into and through the terminal web region. Biochemical studies of brush border contractile proteins suggest that the observed microvillar contraction is actomyosin mediated. We have shown previously that the major protein of the brush border's actin (Tilney, L. G., and M. S. Mooseker. 1971. Proc. Natl. Acad. Sci. U. S. A. 68:2611-2615). The brush border also contains a protein with the same molecular weight as the heavy chain subunit of myosin (200, 000 daltons). In addition, preparations of demembranated brush borders exhibit potassium-EDTA ATPase activity of 0.02 mumol phosphate/mg-min (22 degrees C); this assay is diagnostic for myosin-like ATPase isolated from vertebrate sources. Other proteins of the brush border include a 30,000 dalton protein with properties similar to those of tropomyosin, and a protein with the same molecular weight as the Z band protein, alpha-actinin (95,000 daltons). How these observations bear on the basis for microvillar movements in vivo is discussed within the framework of our recent model for the organization of actin and myosin in the brush border (Mooseker, M. S., and L. G. Tilney. 1975. J. Cell Biol. 67:725-743).  (+info)

(6/139) Biological, biochemical, and physicochemical evidence for the existence of the polyadenylic-polyuridylic-polyinosinic acid triplex.

When primary rabbit kidney cell cultures are treated with either polyadenylic acid-polyuridylic acid or polyadenylic acid-polyribothymidylic acid (poly(rT)) and then judiciously exposed to actinomycin D and cycloheximide, high titers of interferon are found in the extracellular medium ("superinduction") (Vilcek, J. (1970) Ann. N. Y. Acad. Sci. 173, 390-403; Tan, Y. H., Armstrong, J. A., Ke, Y. H., and Ho, M. (1970) Proc. Natl. Acad. Sci. U. S. A. 67, 464-471). If polyinosinic acid is added 1 hour prior to, simultaneously with, or 1 hour after the active interferon inducers, dramatic reductions in interferon production from the "superinduced" cells result. Based on experiments involving sucrose gradient ultracentrifugation, pancreatic ribonuclease A resistance, ultraviolet mixing curves, and ultraviolet absorbance-temperature profiles, the explanation for this phenomenon was determined to be the formation of polynucleotide triplexes in the following way: poly(A)-poly(U) + poly(I) yields poly(A)-poly(U)-poly(I)poly(A)-poly(rT) + poly(I) yields poly(A)-poly(rT)-poly(I). In addition, based on similar methodology, the following reactions involving these triplexes were demonstrated: poly(A)-2 poly(I) + poly(U) yields poly(A)-poly(U)-poly(I) + poly(I)poly(A)-2 poly(I) + poly(rT) yields poly(A)-poly(rT)-poly(I) + poly(I)POLY(A)-2 poly(I) + 2 poly(U) yields poly(A)-2 poly(U) + 2 poly(I) and POLY(A)-poly(U)-poly(I) + poly (U) yields poly(A)-2 poly(U) + poly(I).  (+info)

(7/139) Calcium regulation in chicken gizzard muscle and inosine triphosphate-induced superprecipitation of skeletal acto-gizzard myosin.

Inosine triphosphate (ITP) does not serve as a substrate for myosin light-chain kinase from gizzard muscle. That is to say, myosin light-chain is not phosphorylated in ITP media. Nevertheless, at pH 6.8, 1 mM or 5 mM ITP induces superprecipitation of skeletal acto-gizzard myosin. The ITP-induced superprecipitation occurs in the absence or presence of calcium ions, and regardless of whether gizzard myosin is phosphorylated or not. On the other hand, at pH 8, 5 MM ITP induces practically no superprecipitation of skeletal acto-gizzard unphosphorylated myosin, whereas it does induce a strong superprecipitation of skeletal acto-gizzard phosphorylated myosin. Superprecipitation is also independent of the presence or absence of calcium ions.  (+info)

(8/139) Synthetic analogues of polynucleotides. (Part) XIV. The synthesis of poly (3'-0-carboxymethyl-2'-deoxycytidine) and its interaction with polyinosinic acid.

Poly (3'-O-carboxymethyl-2'-deoxyctidine) (VII) has been synthesised by the polymerisation of 3'-O-carboxymethyl-4-N-phenoxyacety-2'-deoxycytidine (V) and removal of the phenoxyacetyl groups under acidic conditions. V was obtained by the action of 2,4-dinitrophenyl phenylacetate on 3'-O-carboxymethyl-5'-O-triphenylmethyl-2'-deoxycytidine (III) followed by removal of the triphenylmethyl group under carefully controlled acidic conditions. The polymer, VII gave a hypochromic effect of about 20% at 250nm when mixed with poly (1) in 0.2Macetate, pH 5.0. It appeared, therefore, that a complex was formed. Upon heating a solution of this complex there was an initial decrease in optical density followed by a much larger increase to give a Tm of about 60 degrees. Attempts to form the 3'-O-carboxymethyl derivative of 4-N-phenoxyacetyl-5'-O-'triphenylmethyl-2'-deoxycytidine to give a shorter synthetic route to VII were not successful. 3'-O-Carboxymethyl-2'-deoxycytidine was obtained by removal of thetriphenylmethyl group from III. Attempts to polymerise this compound in concentrated aqueous solution with a water-soluble carbodiimide were not successful.  (+info)