bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct method for detection and characterization of cell surface receptors for insulin by means of 125I-labeled autoantibodies against the insulin receptor.
Authors: Jarrett D B , Roth J , Kahn C R , Flier J S
Published: May 2006

Autoantibodies directed against the cell surface receptors for insulin are found in some patients with extreme insulin resistance. These antibodies specifically inhibit the binding of insulin to its receptor. A purified IgG fraction from one patient's plasma was labeled with 125I. The 125I-labeled antireceptor antibody, which initially represented about 0.3% of the total 125I-IgG, was enriched by selective adsorption and subsequent elution from cells rich in insulin receptors. The 125I-antireceptor antibody bound to cells and the binding was inhibited by whole plasma and purified IgG from this patient, as well as whole plasma from another patient with autoantibodies to the insulin receptor. Insulins that differed 300-fold in biological potency and affinity inhibited binding of 125I-antireceptor antibody in direct proportion to their ability to bind to the insulin receptor. The binding of 125I-antireceptor antibody was closely correlated with the binding of 125I-insulin over a wide range of receptor concentrations on different cell types. Experimentally induced reduction of the insulin receptor concentration was associated with parallel decreases in the binding of 125I-antireceptor antibody and 125I-insulin. The preparation of 125I-antireceptor antibody with a high specific activity by cytoadsorption and elution has provided a sensitive method for the detection of receptors and autoantibodies to cell surface components.
beta-Endorphin: cross tolerance to and cross physical dependence on morphine.
Authors: Tseng L F , Loh H H , Li C H
Published: May 2006

The effects of beta-endorphin on the antinociceptive responses and abrupt withdrawal jumping in morphine-dependent mice were studied. Mice were rendered morphine dependent by implantation of a morphine pellet (75 mg base) for 3 days. The analgesic response to beta-endorphin decreased after morphine pellet implantation, as evidenced by an eight-fold increase in the median antinociceptive dose of morphine was found. In small doses (0.09-0.17 mug per mouse), beta-endorphin suppressed abrupt withdrawal jumping. Met-enkephalin, even in high doses (200 mug per mouse), did not suppress abrupt withdrawal jumping.
Dichloromethane as an antisickling agent in sickle cell hemoglobin.
Authors: Schoenborn B P
Published: May 2006

Microscopic studies of red cells from homozygous sickle cell patients show that dichloromethane does prevent sickle cell formation in vitro and does cause reversion of sickled cells to normal after exposure to dichloromethane. X-ray structural analysis of human deoxyhemoglobin crystals exposed to dichloromethane shows four unique binding sites. Arguments are presented to suggest that the binding site close to tryptophan 14alpha prevents the formation of helical polymers, i.e., prevent sickling.
Modeling the resonance Raman spectrum of a metarhodopsin: implications for the color of visual pigments.
Authors: Sulkes M , Lewis A , Lemley A T , Cookingham R
Published: May 2006

Resonance Raman spectra of an invertebrate rhodopsin are reported. The spectrum of squid acid metarhodopsin is compared with the spectra of model compounds of the retinylidene chromophore in the all-trans conformation. Correlations made between acid metarhodopsin and these crystalline model compounds with known x-ray structures indicate that the chromophore in this intermediate is an all-trans protonated Schiff base. The data suggest a mechanism for the red shift in rhodopsin.
Structural characterization of a bridged 99Tc-Sn-dimethylglyoxime complex: implications for the chemistry of 99mTc-radiopharmaceuticals prepared by the Sn (II) reduction of pertechnetate.
Authors: Deutsch E , Elder R C , Lange B A , Vaal M J , Lay D G
Published: May 2006

Reduction of pertechnetate by tin(II) in the presence of dimethylglyoxime is shown, by single crystal x-ray analysis, to yield a technetium-tin-dimethylglyoxime complex in which tin and technetium are intimately connected by a triple bridging arrangement. One bridge consists of a single oxygen atom and it is hypothesized that this bridge arises from the inner sphere reduction of technetium by tin(II), the electrons being transferred through a technetium "yl" oxygen which eventually becomes the bridging atom. Two additional bridges arise from two dimethylglyoxime ligands that function as bidentate nitrogen donors towards Tc and monodentate oxygen donors towards Sn. The tin atom can thus be viewed as providing a three-pronged "cap" on one end of the Tc-dimethylglyoxime complex. The additional coordination sites around Tc are occupied by the two nitrogens of a third dimethylglyoxime ligand, making the Tc seven-coordinate. The additional coordination sites around Sn are occupied by three chloride anions, giving the Sn a fac octahedral coordination environment. From indirect evidence the oxidation states of tin and technetium are tentatively assigned to be IV and V, respectively. Since most 99mTc-radiopharmaceuticals are synthesized by the tin(II) reduction of pertechnetate, it is likely that the Sn-O-Tc linkage described in this work is an important feature of the chemistry of these species. This linkage also provides a ready rationale for the close association of tin and technetium observed in many 99mTc-radiopharmaceuticals.
A large product of cell-free translation of messenger RNA coding for corticotropin.
Authors: Nakanishi S , Taii S , Hirata Y , Matsukura S , Imura H
Published: May 2006

Polyadenylate-containing RNA prepared from the membrane fraction of bovine anterior pituitary gland was shown to direct the synthesis of a large translation product related to corticotropin (adrenocorticotropic hormone) in a cell-free system derived from wheat germ. This product was identified by immunoprecipitation with specific antibody against corticotropin, followed by electrophoretic analysis of the dissociated immunoprecipitate on sodium dodecyl sulfate-polyacrylamide gel. Further evidence for the identity of the translation product was provided by the presence of a common peptide in the chymotryptic digest of [35S]methionine-labeled cell-free product and in that of authentic corticotropin. The molecular weight of the translation product was estimated to be approximately 35,000, based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results indicate that corticotropin messenger RNA directs the cell-free synthesis of a product that contains the amino acid sequence of corticotropin but is much larger than this hormone.
Interactions of heterologous nitrogenase components that generate catalytically inactive complexes.
Authors: Emerich D W , Burris R H
Published: May 2006

A unique method is described for inhibiting nitrogenase. When Clostridium pasteurianum nitrogenase is assayed in the presence of the Mo-Fe protein of Azotobacter vinelandii, all the characteristic activities of nitrogenase are inhibited. C. pasteurianum nitrogenase is unaffected by the Fe protein of A. vinelandii. The Fe protein, but not the Mo-Fe protein of C. pasteurianum, inhibits A. vinelandii nitrogenase. Both inhibitions described result from the formation of an inactive complex of A. vinelandii Mo-Fe protein and C. pasteurianum Fe protein. Complex formation requires active components, as oxygen-denatured proteins are ineffective. The results for titration of components of the complex against each other and kinetic data each indicate that the inactive complex consists of two molecules of C. pasteurianum Fe protein per molecule of A. vinelandii Mo-Fe protein. The results of kinetic experiments suggest that the Fe protein from each organism competes for the same site(s) on the A. vinelandii Mo-Fe protein. The Fe protein of C. pasteurianum will form an active or an inactive complex with the Mo-Fe proteins from six different organisms. Inhibition by nitrogenase components that form inactive complexes provides numeroius ways to study the mechanism of nitrogenase action.
Hydrolysis of nicotinamide adenine dinucleotide by choleragen and its A protomer: possible role in the activation of adenylate cyclase.
Authors: Moss J , Manganiello V C , Vaughan M
Published: May 2006

Choleragen and the isolated A protomer catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. The protein with NADase activity (NAD nucleosidase; NAD glycohydrolase, EC 3-2-2-5) migrated on polyacrylamide gels with choleragen, and chromatographed on Bio-Gel P-60 columns with the A protomer. The NADase activity of choleragen and of the A protomer was increased markedly in acetate and phosphate buffers, and enhanced over 10-fold by dithiothreitol in high concentration. NAD hydrolysis was proportional to choleragen concentration; the Michaelis constant for NAD was about 4 mM with both choleragen and the A protomer. The demonstration that the A protomer of choleragen catalyzes an enzymatic reaction involving activation of the ribosyl-nicotinamide bond of NAD, a reaction analogols to those catalyzed by diphtheria toxin, supports the hypothesis that activation of adenylate cyclase by choleragen involves the ADP-ribosylation of an appropriate acceptor protein.
Path of electrons in photosynthesis
Authors: Arnold William
Published: May 2006

Electrons, from the oxidation of water, inside the grana disks (thylakoids) are transferred across the membrane to the outside, to the Calvin cycle or the Hill oxidant. The span in redox level may be 2.3 V. Part of the system II chlorophyll is on the inside of the membrane and part on the outside. An electron trap is embedded in the membrane. Alternately, an excited chlorophyll on the inside gives an electron to the trap, and an excited chlorophyll on the outside gives a hole to the trap. Two quanta move an electron from inside to outside. The charging of this condenser drives the redox levels on the inside positive and those on the outside negative. The final voltages depend upon the electron flow and a carotene diode. A voltage of 0.3 is involved. Delayed light is the exact reverse of the light reaction. System I makes ATP.
DNA-relaxing activity and endonuclease activity in Xenopus laevis oocytes.
Authors: Mattoccia E , Attardi D G , Tocchini-Valentini G P
Published: May 2006

Complex simian virus 40 DNA produced by a soluble cell-free extract derived from stage 6 oocytes of Xenopus laevis consists of fully relaxed circles (i.e., with no superhelical turns). An endonuclease and a DNA-relaxing protein, either or both of which could be responsible for the relaxation of the complex DNA, have been purified from the extract. The endonuclease(s) produces nicked circles (having a single-strand scission) and linear full-size molecules. The DNA-relaxing protein is in the nucleus, has a molecular weight of apporximately 70,000, and is able to remove both negative and positive superhelical turns.
Analysis of HeLa cell hypoxanthine phosphoribosyltransferase mutants and revertants by two-dimensional polyacrylamide gel electrophoresis: evidence for silent gene activation.
Authors: Milman G , Lee E , Ghangas G S , McLaughlin J R , George M
Published: May 2006

The spot corresponding to hypoxanthine phosphoribosyltransferase (HPRT; IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) has been identified in two-dimensional polyacrylamide gels of HeLa cell extracts. This spot is absent in gels of 24 HPRT dificient mutants. A missense mutant displays a new HPRT spot at the same molecular weight but different isoelectric focusing position. Five independently isolated revertants of the missense mutant display spots corresponding to both the wild-type and mutant proteins indicating that they synthesize HPRT from two separate genes. If the missense protein is synthesized from a mutated form of the initially active HPRT gene, then wild-type HPRT protein in the revertants must be snythesized from a newly activated but prevously silent wild-type gene. The newly activated gene in the revertants of the missense mutation appears unstable producing a high frequency of spontaneous HPRT mutants.
Changes in expression of murine leukemia virus antigens and production of xenotropic virus in the late preleukemic period in AKR mice.
Authors: Kawashima K , Ikeda H , Hartley J W , Stockert E , Rowe W P , Old L J
Published: May 2006

We recently reported that thymocytes from 6-month-old preleukemic AKR mice express higher levels of murine leukemia virus (MuLV)-related antigens that thymocytes from 2-month-old mice. We have now found that the level of xenotropic MuLV (defined operationally as MuLV able to infect mink cell cultures) is also markedly increased in thymus of 6-month-old AKR mice and that this increase in virus correlates closely with increased MuLV-antigen expression. There is no increase of MuLV antigen or xenotropic virus in spleen or lymph nodes. Production of ecotropic MuLV remains unchanged with age in thymus, lymph nodes, and spleen. Thymic grafts from 6-month-old AKR mice, but not from 2-month-old mice, induce both amplified MuLV-antigen expression and xenotropic virus production in the thymus of young AKR recipients. Experiments with lethally irradiated AKR mice reconstituted with syngeneic bone marrow cells indicate that age-related changes in the thymus rather than in bone marrow precursor cells are responsible for MuLV-antigen amplification.
Fluorescence-detected magnetic circular dichroism of fluorescent and nonfluorescent molecules.
Authors: Sutherland J C , Low H
Published: May 2006

We have modified a spectrometer for the measurement of fluorescence-detected magnetic (and natural) circular dichroism (FDMCD). The instrument can be operated either in a direct mode in which the average and polarization-induced differential fluorescent intensities are recorded separately or in a mode which records their ratio. We have measured the FDMCD of tryptophan, which is itself fluorescent. With the aid of an added fluorescent molecule we also measured the FDMCD of Fe(III) cytochrome c, which is nonfluorescent. In both cases, the FDMCD agreed with the conventional transmission-detected magnetic circular dichroism within experimental uncertainty. The FDMCD of both fluorescent and nonfluorescent molecules is potentially a useful technique for investigating optically dense materials and biological molecules in their native environments and systems in which there is inter- or intramolecular energy transfer.
Maximally dependent random variables
Authors: Lai T. L. , Robbins Herbert
Published: May 2006

Let
X
1
,...,

X
n

have an arbitrary common marginal distribution function
F
, and let

M
n

= max(
X
1
,...,

X
n

). It is shown that

EM
n

≤

m
n

, where

m
n

=

a
n

+
n
[unk]

an

∞
[1 -
F
(
x
)]
dx
and =
F
-1
(1 -
n
-1
), and that

EM
n

=

m
n

when
X
1
,...,

X
n

are “maximally dependent”; i.e.,
P
(

M
n

>
x
) = min{1,
n
[1 -
F
(
x
)]} for all
x
. Moreover, as
n
→ ∞,

a
n

∼

m
n

∼

m
n

*
, where

m
n

*
=

EM
n

when
X
1
,...,

X
n

are independent, provided that [1 -
F
(
cx
)]/[1 -
F
(
x
)] → 0 as
x
→ ∞ for every
c
> 1, and
E
(
X
1
-
)

r

< ∞ for some
r
> 0. The case in which
F
is standard normal is considered in detail.
Transbilayer distribution and movement of cholesterol and phospholipid in the membrane of influenza virus.
Authors: Lenard J , Rothman J E
Published: May 2006

The transfer of radioactive cholesterol from influenza virus to excess phosphatidylcholine-cholesterol vesicles has been studied. Viral cholesterol was found to exist in two pools, one rapidly exchangeable. Evidence is presented that the rapidly exchangeable pool corresponds to cholesterol present on the outer surface of the viral bilayer, while the slowly exchangeable pool corresponds to inner surface cholesterol. Approximately equal amounts are present in each pool, suggesting that cholesterol distribution is not markedly asymmetric in the viral bilayer. A half-time for the rate of equilibration between the two sides of the bilayer (flip-flop) was about 13 days at 37 degrees with a 90% confidence interval of 3.4- infinity days. Similar experiments were carried out which followed the time course of transfer of labeled phospholipids from the viral bilayer to phospholipid vesicles, catalyzed by phospholipid exchange protein from beef heart. From these experiments the half-times for the flip-flop of phosphatidyl-choline and spingomyelin were found to be indeterminately in excess of 10 and 30 days at 37 degrees, respectively. These results suggest that exchange of the major components of the viral bilayer between the two surfaces occurs very slowly relative to the turnover times of most membrane constituents, and provide a plausible mechanism for the maintenance of membrane asymmetry over biologically relevant time periods.
Biliproteins of cyanobacteria and Rhodophyta: Homologous family of photosynthetic accessory pigments
Authors: Glazer Alexander N. , Apell Gerald S. , Hixson Craig S. , Bryant Donald A. , Rimon Sara , Brown Douglas M.
Published: May 2006

Amino-terminal sequence determinations are reported of the subunits of biliproteins of prokaryotic unicellular and filamentous cyanobacteria and of eukaryotic unicellular red algae. The biliproteins examined, allophycocyanin, C-phycocyanin, R-phycocyanin, b-phycoerythrin, and phycoerythrocyanin, vary with respect to the chemical nature and the number and distribution of the bilin chromophores between the two dissimilar subunits. The amino-terminal sequences fall into two classes, “α-type” and “β-type”, with a high degree of homology within each class.

In those biliproteins where the number of bilin chromophores on the two subunits is unequal, the subunit with the greater number of chromophores has the β-type amino-acid sequence.

Extensive homology also exists between α- and β-type sequences, strongly supporting the view that these arose by gene duplication to give rise to the ancestral α- and β-type genes early in the evolution of the biliproteins. The subsequent generation of the various classes of biliproteins appears to be the result of further gene duplication of the α- and β-type genes, ultimately to give rise to families of polypeptide chains of similar sequence, but varying in the number of chromophore attachment sites and the structure of the chromophores.
Molecular orbital studies of enzyme activity: catalytic mechanism of serine proteinases.
Authors: Scheiner S , Lipscomb W N
Published: May 2006

The catalytic activity of the serine proteinases is studied using molecular orbital methods on a model of the enzyme-substrate complex. A mechanism is employed in which Ser-195, upon donating a proton to the His-57-Asp-102 dyad, attacks the substrate to form the tetrahedral intermediate. As His-57 then donates a proton to the leaving group, the intermediate decomposes to the acyl enzyme. An analogous process takes place during deacylation, as a water molecule takes the place of Ser-195 as the nucleophile. The motility of the histidine is found to be an important factor in both steps. An attempt is made to include the effects of those atoms not explicitly included in the calculations and to compare the reaction rate of the proposed mechanism with that of the uncatalyzed hydrolysis. This mechanism is found to be in good agreement with structural and kinetic data.
Application of polarization effects in light scattering: a new biophysical tool.
Authors: Bickel W S , Davidson J F , Huffman D R , Kilkson R
Published: May 2006

We demonstrate that a newly developed instrument which measures all polarization and intensity information contained in differentially and elastically scattered light has valuable applications in biology. The polarization states of light scattered differentially from suspensions of biological scatters are shown to contain structural information about those systems. The scatterers are discussed in the context of a 16 component matrix which completely characterizes the scattering process. The instrument and method are described in terms of the corresponding matrix algebra. We also discuss the use of the instrument as a device for distinguishing between closely related structural systems and as a tool for following time-dependent structural changes.
Structure and evolution of transplantation antigens: partial amino-acid sequences of H-2K and H-2D alloantigens.
Authors: Silver J , Hood L
Published: May 2006

Techniques for the amino acid sequence analysis of subnanomole quantities of polypeptides have been applied to characterize beta2-microglobulin and transplantation antigens of the mouse isolated from spleen cells by indirect immunoprecipitation. Eleven residues were identified throughout the NH2-terminal 27 residues of the beta2-microglobulin; all were identical to residues seen at the corresponding positions of beta2-microglobulins from other species. Two K and two D transplantation antigens were examined and the following generalizations emerged from the limited partial amino-acid sequence data: (1) the K and D molecules are homologous to one another; (2) they do not show amino acid sequence homology with immunoglobulins; (3) the two K and two D molecules differ from one another by multiple amino acid substitutions; and (4) the K molecules as a class cannot be distinguished from the D molecules as a class. The genetic and evolutionary implications of these observations are discussed.
Attempts to locate residues in complementarity-determining regions of antibody combining sites that make contact with antigen.
Authors: Kabat E A , Wu T T , Bilofsky H
Published: May 2006

From collected data on variable region sequences of heavy chains of immunoglobulins, the probability of random associations of any two amino-acid residues in the complementarity-determining segments was computed, and pairs of residues occurring significantly more frequently than expected were selected by computer. Significant associations between Phe 32 and Tyr 33, Phe 32 and Glu 35, and Tyr 33 and Glu 35 were found in six proteins, all of which were mouse myeloma proteins which bound phosphorylcholine (= phosphocholine). From the x-ray structure of McPC603, Tyr 33 and Glu 35 are contacting residues; a seventh phosphorylcholine-binding mouse myeloma protein also contained Phe 32 and Tyr 33 but position 35 had only been determined as Glx and thus this position had not been selected. Met 34 occurred in all seven phosphorylcholine-binding myeoma proteins but was also present at this position in 29 other proteins and thus was not selected; it is seen in the x-ray structure not to be a contacting residue. The role of Phe 32 is not obvious but it could have some conformational influence. A human phosphorylcholine-binding myeloma protien also had Phe, Tyr, and Met at positions 32, 33, and 34, but had Asp instead of Glu at position 35 and showed a lower binding constant. The ability to use sequence data to locate residues in complementarity-determing segments making contact with antigenic determinants and those playing essentially a structural role would contribute substantially to the understanding of antibody specificity.
Activation of an endogenous mouse type C virus by ultraviolet-irradiated herpes simplex virus types 1 and 2.
Authors: Hampar B , Aaronson S A , Derge J G , Chakrabarty M , Showalter S D , Dunn C Y
Published: May 2006

Infection of BALB/c mouse cells with UV-irradiated herpes simplex virus (HSV) types 1 and 2 resulted in activation of a xenotropic type C virus detected by infectious center formation in permissive rat cells. The levels of type C virus activated by HSV were related to the UV dose and the multiplicity of infection used. The ability of HSV to activate type C virus was eliminated by heat-inactivation and by neutralization with specific antiserum against HSV, but was not affected by purification or treatment with DNase and RNase. Maximum levels of type C virus in the cells and medium were observed within 1 day after HSV infection, and the levels returned to control cell values within 3-4 days. The possible significance of these findings with respect to the putative oncogenic potential of HSV is discussed.
Determination of nucleotide sequences beyond the sites of transcriptional termination.
Authors: Rosenberg M , de Chrombrugghe B , Musso R
Published: May 2006

A procedure is described by which a discrete high-molecular-weight RNA transcription product can be used as a primer by DNA polymerase (DNA nucleotidyltransferase; EC 2.7.7.7; deoxynucleoside triphosphate: DNA deoxynucleotidyltransferase) for determining nucleic acid sequence in the template DNA beyond the 3'-terminus of the transcript. This procedure is applied to two lambda phage transcripts, the 4S "oop" RNA [Short l-strand RNA transcript from the region of origin of replication (ori) and the 6S RNA. Sequences of 35 and 19 nucleotides, respectively, following the sites at which these two transcripts terminate, are determined. Little structural homology is apparent in the template DNA beyond the 3'-ends of these two transcripts. The lack of homology suggests that this region might not be important to the termination process.
No detectable reiteration of genes coding for mouse MOPC 41 immunoglobulin light-chain mRNA.
Authors: Farace M G , Aellen M F , Briand P A , Faust C H , Vassalli P , Mach B
Published: May 2006

RNA fractions rich in immunoglobulin light (L)-chain mRNA were isolated from mouse myeloma MOPC 41 by procedures previously described, and chemically labeled with 125I. These RNA fractions were hybridized with MOPC 41 DNA under conditions of DNA excess. Hybridization conditions were chosen under which the entire sequence of the L-chain mRNA probe, thus including the variable region, remains available for hybridization throughout the reaction. The hybridization (C0t) curve showed double transition kinetics, with one component corresponding to about 250 gene copies and the other to about two to four copies. In contrast, when MOPC 41 L-chain mRNA was further purified as a single band by gel elecptrophoresis in 99% formamide, the hybridization curve showed only a single transition, corresponding to about two to four genes, with the disappearance of the "reiterated" component. That component resulted therefore from contaminating RNA species. The data indicate that no reiteration can be detected by RNase or by hydroxylapatite for the genes corresponding to the entire sequence of MOPC 41 L-chain mRNA, including the untranslated segments, within the limits of detectability of short reiterated segments. It thus appears that there is only one or very few genes corresponding to the 41 L-chain variable region "subgroup" in MOPC 41 DNA. The possibility that the variable genes of plasmocytes might result frm a combination of several nonreiterated germline genes is discussed.
Isolation of an intermediate which precedes dnaG RNA polymerase participation in enzymatic replication of bacteriophage phi X174 DNA.
Authors: Weiner J H , McMacken R , Kornberg A
Published: May 2006

Conversion of phi X174 single-stranded DNA to the duplex replicative form (RF) in vitro requires at least 10 purified proteins. Three stages - strand initiation, elongation, and termination - comprise this conversion. We now identify a separate stage in strand initiation which precedes dnaG RNA polymerase participation. Incubation of five proteins - protein i, protein n, DNA unwinding protein, dnaB protein, and dnaC protein - with ATP and phi X174 DNA forms an intermediate which enables subsequent stages measured by DNA synthesis to proceed 20 times faster. The intermediate can be isolated in quantitative yield by gel filtration or by ultracentrifugation. Protein i and protein n are required in less than stoichiometric amounts and appear to be absent from the isolated intermediate. Whereas formation of the intermediate is sensitive to antibody to protein i and to N-ethylmaleimide (an inhibitor of protein n and dnaC protein), the intermediate itself is resistant to these reagents. DNA unwinding protein complexes the DNA in a ratio of 60 molecules per circle. Synthesis of the intermediate appears to require stoichiometric quantities of dnaB protein and dnaC PROTEin but their presence in the intermediate has not been established as yet.
Solid tumor models for the assessment of different treatment modalities: systematics of response to radiotherapy and chemotherapy.
Authors: Looney W B , Trefil J S , Schaffner J G , Kovacs C J , Hopkins H A
Published: May 2006

The change of tumor volumes (efficiency) with local tumor radiation doses from 375R to 3750R and 5-fluorouracil (5-FUra) from 50 to 250 mg/kg was assessed in rats bearing hepatoma 3924A. The data were analyzed utilizing a chi2 technique which fits the logarithmic volume response to polynomials. This provided greater flexibility in selecting different mathematical forms, and allows more accurate description of tumor changes after treatment than the least squares analysis previously used. Quantitative information can be obtained on one tumor following treatment by this method. This information is more analogous to the management of a patient with a solid tumor. The results show a continuous increase in efficiency of radiation throughout the radiation dose range from 375R to 3750R. The efficiency of 5-FUra increased slightly but did not continue to increase with doses of 5-FUra higher than 150 mg/kg. This suggests that factors such as toxicity to the host may prevent further increases of the effectiveness of 5-FUra. The time of minimum tumor volume change after radiation was approximately 6 days and for 5-FUra, 6 days. The time for maximum tumor volume change for 5-FUra was 12 days. There was a slight trend upward for maximum growth for increasing radiation doses from 18 to 22 days. The time of occurrence of both minimum and maximum tumor volume change after treatment showed little relationship to increasing doses of radiation and 5-FUra. Parallel studies have shown that the maximum rate of tumor volume change occurs shortly after the recovery of the host from the effect of 5-FUra. It is feasible, therefore, to use chemotherapy alone or in combination with radiotherapy, and optimize the scheduling of these treatment modalities with recovery of the host from previous therapy.
Bovine leukemia virus: an exogenous RNA oncogenic virus.
Authors: Kettmann R , Portetelle D , Mammerickx M , Cleuter Y , Dekegel D , Galoux M , Ghysdael J , Burny A , Chantrenne H
Published: May 2006

Short-term cultures of bovine leukemic lymphocytes release virus particles with biochemical properties of RNA oncogenic viruses. These particles, tentatively called bovine leukemia virus (BLV), have a high molecular weight RNA-reverse transcriptase complex and a density of 1.155 g/ml in sucrose solutions. Molecular hybridizations between BLV/[3H]cDNA and several viral RNAs show that BLV is not related to Mason-Pfizer monkey virus, simian sarcoma associated virus, feline leukemia virus, or avian myeloblastosis virus. These results were confirmed by hybridization between BLV 70S RNA and [3H]cDNA synthesized in the various viruses tested. The high preference of BLV reverse transciptase for Mg++ as the divalent cation suggests that BLV might be an atypical mammalian leukemogenic "type C" virus. DNA-DNA hybridization studies using BLV [3H]cDNA as a probe strongly suggest that the DNA of bovine leukemic cells contains viral sequences that cannot be detected in normal bovine DNA.
Integrated simian virus 40 sequences in transformed cell DNA: analysis using restriction endonucleases.
Authors: Ketner G , Kelly T J
Published: May 2006

The DNAs from five independent simian virus 40 (SV40) transformants of the BALB/c3T3 mouse cell line were digested with either the HpaII or the BamHI restriction endonuclease and the resulting fragments were fractionated by gel electrophoresis. The DNA fragments were denatured in situ in the gel and transferred to a membrane filter. Fragments containing viral DNA were detected by hybridization with high specific activity 32P-labeled SV40 complementary RNA (cRNA) synthesized in vitro. Each of the lines yielded a small number of fragments containing SV40 DNA and the fragments from each line were different. This observation shows that the structure of the integrated SV40 DNA and/or its location in the host DNA are different in each line.
Specific release of the thioesterase component of the fatty acid synthetase multienzyme complex by limited trypsinization.
Authors: Smith S , Agradi E , Libertini L , Dileepan K N
Published: May 2006

Limited trypsinization of the fatty acid synthetase multienzyme complex from rat mammary gland results in the release of a protein, molecular weight 32,000, with thioesterase activity. The other components of the multienzyme complex--the acyl carrier protein, acetyl and malonyl transferases, condensing enzyme, keto reductase, dehydrase and enoyl reductase--are not affected and remain associated with the complex. The thioesterase can be isolated by ammonium sulfate precipitation and gel filtration. Extensive trypsinization of fatty acid synthetase multienzyme complex results in a loss of thioesterase activity, probably due to cleavage of the thioesterase component into inactive peptides. However, the molecular weight and specific activity of the thioesterase isolated after limited trypsinization is relatively unaffected by the severity of the conditions of proteolysis. Both the thioesterase and the residual trypsinized complex react with antibodies produced against the native multienzyme. The results demonstrate that mild trypsinization can be used to release the thioesterase component of the multienzyme with little perturbation of either the thioesterase or the other components of the complex.
Activation of 3':5'-cyclic AMP-dependent protein kinase and induction of ornithine decarboxylase as early events in induction of mixed-function oxygenases.
Authors: Byus C V , Costa M , Sipes I G , Brodie B B , Russell D H
Published: May 2006

The parenteral administration of a single dose of 3-methylcholanthrene to rats caused an increase in the liver of the concentration of 3', 5'-cAMP and of the activity of cAMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37). These events were followed by an increased activity of ornithine decarboxylase (L-ornithine carboxy-lase, EC 4.1.1.17), the enzyme that controls the biosynthesis of polyamines. Finally, the activity of benzo[a]pyrene hydroxylase, as well as the amount of cytochrome P-448, was increased. Similarly, after the administration of phenobarbital, there was first an increase in the cAMP concentration and in the activity of cAMP-dependent protein kinase, then the induction of ornithine decarboxylase, and finally, an enhanced activity of ethylmorphine N-demethylase and an increased content of cytochrome P-450. These data suggest that the drug-induced processes in liver that increase the activities of the oxidative, and presumably other, drug-metabolizing enzymes include the following sequence of events: (1) increase in cAMP concentration and/or activation of cAMP-dependent protein kinase; (2) induction of ornithine decarboxylase; and, (3) induction of drug-metabolizing enzymes.
Antisera against electrophoretically purified tubulin stimulate colchicine-binding activity.
Authors: Aubin J E , Subrahmanyan L , Kalnins V I , Ling V
Published: May 2006

Several rabbit antisera have been prepared against reduced and alkylated, electrophoretically purified tubulin isolated from chick brain. These antisera give a single precipitin line in Ouchterlony double diffusion plates when tested against partially purified tubulin, and label specifically microtubule- and tubulin-containing structures, such as mitotic spindles, cilia, and vinblastine-induced crystals, in a variety of cells. The same antisera also display the unique ability to stimulate the colchicine-binding activity of tubulin preparations from chick brain and Chinese hamster ovary tissue culture cells. This specific stimulation of colchicine binding activity is also obtained with the gamma globulin fractions purified by ammonium sulfate precipitation of these antisera.
Hypertrophy and hyperplasia of somatostatin-containing D-cells in diabetes.
Authors: Orci L , Baetens D , Rufener C , Amherdt M , Ravazzola M , Studer P , Malaisse-Lagae F , Unger R H
Published: May 2006

Insulin-, glucagon-, and somatostatin-contianing cells, identified by immunofluorescent staining, were quantitated morphometrically in sections of pancreas obtained from diabetic and nondiabetic humans and rats. Both the volume density and number of somatostatin- and glucagon-containing cells were significantly increased in the islets of juvenile-type human diabetics and of streptozotocin diabetic rats.
The solid phase synthesis of a protein activator for lecithin-cholesterol acyltransferase corresponding to human plasma apoC-I.
Authors: Sigler G F , Soutar A K , Smith L C , Gotto A M , Sparrow J T
Published: May 2006

Apolipoprotein C-I, a protein constituent of the very low density lipoproteins of human plasma, consists of a single chain of 57 amino acids. The total synthesis of a protein corresponding to apolipoprotein C-I in physical properties and compositions was accomplished by solid phase techniques employing a modified polystrene incorporating spacer groups between the point of attachment of the first residue and the polymer matrix. The synthetic apoprotein was shown to activate lecithin:cholesterol acyltransferase to the same extent as the native protein. Comparative lipid-binding studies with dimyristoyl phosphatidylcholine gave complexes for native and synthetic apoprotein which floated at the same density after ultracentrifugation in KBr gradients and had virtually the same lipid:protein ratios.
Desensitization of beta-adrenergic receptors by beta-adrenergic agonists in a cell-free system: resensitization by guanosine 5'-(beta, gamma-imino)triphosphate and other purine nucleotides.
Authors: Mukherjee C , Lefkowitz R J
Published: May 2006

Incubation of purified frog erythrocyte membranes with beta-adrenergic agonists at 25 degrees produces relatively rapid (half-time about 10 min) desensitization (inactivation) of about 60% of the beta-adrenergic receptor binding sites. The desensitized receptors no longer bind the specific beta-adrenergic ligand (-)[3H]dihydroalprenolol. The decrease in the number of functional beta-adrenergic receptors is also manifest as a decreased ability of isoproterenol to stimulate the membrane-bound adenylate cyclase.
Hepatic phenylalanine 4-monooxygenase is a phosphoprotein.
Authors: Milstien S , Abita J P , Chang N , Kaufman S
Published: May 2006

Phenylalanine hydroxylase [phenylalanine 4-monooxygenase; EC 1.14.16.1; L-phenylalanine, tetrahydropteridine:oxygen oxidoreductase(4-hydroxylating)] isolated from rat liver is a phosphoprotein containing approximately 0.31 mumol of protein-bound phosphate per mumol of subunit (50,000 molecular weight). When the enzyme is further phosphorylated in the presence of ATP and a 3'5'-cyclic-AMP-dependent protein kinase (EC 2.7.1.37; ATP:protein phsophotransferase), an additional 0.7 mumol of phosphate per mumol of subunit is introduced, bringing the total phosphate content up to about 1 mumol/mumol of subunit. This phosphorylation of the enzyme in vitro is accompanied by a 2.6-fold increase in hydroxylase activity when the activity is assayed in the presence of tetrahydrobiopterin. Partial proteolytic digestion of phenylalanine hydroxylase, which previously had been shown to activate the enzyme 20- to 50-fold [Fisher, D.B. & Kaufman, S. (1973) J. Biol. Chem. 248, 4345-4353], removes almost all of the phosphate from the enzyme.
Demonstration of an idiotypic antigen on a monoclonal cold agglutinin and on its isolated heavy and light chains.
Authors: Kobzik L , Brown M C , Cooper A G
Published: May 2006

A potent anti-idiotype serum produced in a rabbit immunized with the isolated heavy chains of an IgM cold agglutinin "Col" was rendered specific by solid-state adsorptions. The anit-Col idiotype was shown to bind specifically to both isolated Col heavy (mu) and light (kappa) chains as well as to intact Col IgM by three methods: (i) reversal of anti-idiotype inhibition of Col cold agglutinin in an automated hemagglutination-inhibition assay system; (ii) adsorption of the anti-idiotype by affinity gels consisting of Col IgM, mu, or kappa chains covalently coupled to Sepharose 2B; (iii) binding of Col IgM and its isolated chains by an anti-idiotype affinity gel. Fragments of Col light chain lacking constant region determinants but still capable of inhibiting anti-idiotype were produced by limited pepsin digestion of the light chains. The finding of shared idiotypic determinants on isolated heavy and light chains of a monoclonal antibody suggests that these chains share a common sequence in a hypervariable region. As an extension of the gene insertion theory of Wu and Kabat, we postulate that genes coding for hypervariable regions may be available for insertion into the DNA for both heavy and light chains.
Antibody-producing cells: virus-induced alteration of response to antigen.
Authors: Riley V , Braun W , Ishizuka M , Spackman D
Published: May 2006

Spleen antibody-forming cells of mice yield a 3- to 10-fold increase in their response to sheep erythrocyte antigen if they are acutely infected by lactate dehydrogenase-elevating virus. This early stimulation is replaced by a long-term inhibition of the antibody-forming cells as the viremia goes into its persisting chronic stage. These contrasting immunological phenomena are examined as contributing factors responsible for the enhancement by this virus of asparaginase (EC 3.5.1.1; L-asparagine amidolydrolase) therapy against leukemia in mice, and for the alteration of the susceptibility of mice to various neoplastic processes.
Localization of acetylcholine receptors during synaptogenesis in retina.
Authors: Vogel Z , Nirenberg M
Published: May 2006

Nicotinic acetylcholine receptors are synthesized in chick embryo retina before synapses appear. Most of the receptors are found associated with neurites in the inner synaptic layer of the retina; later in development the receptors appear in the outer synaptic layer. Cells dissociated from retina and cultured in vitro form aggregates and also sort out into regions comprised either of neurites or cell bodies. Most of the nicotinic acetylcholine receptors of aggregates are found associated with neurite regions. The receptor distribution of cultured retina cells thus resembles that of intact retina.
Poliovirus-induced inhibition of polypeptide initiation in vitro on native polyribosomes.
Authors: Kaufmann Y , Goldstein E , Penman S
Published: May 2006

The inhibition of HeLa cell protein synthesis by poliovirus was studied by examining initiation in vitro on endogenous host polyribosomes. At an early stage, before major viral RNA replication and protein synthesis begins, the initiation of translation on cellular mRNA is strongly inhibited. Fractionation of extracts from infected cells shows that the lesion is associated mainly with the crude polyribosome fraction. The cellular mRNA appears unchanged and is as active as mRNA from control cells in stimulating incorporation. The native ribosomal subunits and KCl-washed polyribosomes from the infected cells are also active. Only the ribosomal wash fraction prepared from the inhibited polyribosomes had reduced activity. However, the reduction in the ribosomal wash activity measured in a reconstructed system is not as large as the inhibition seen with "native" polyribosomes. The results indicate that a viral induced inhibition is probably associated with the ribosomal wash fraction, but the reconstructed system is not equivalent to the "native" inhibited system.
Cyanobacterial DNA-binding protein related to Escherichia coli HU.
Authors: Haselkorn R , Rouvière-Yaniv J
Published: May 2006

A DNA-binding protein has been isolated from two cyanobacteria (blue-green algae): Anabaena sp and Aphanocapsa sp. It has a molecular weight as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis of about 10,000, is rich in lysine and arginine, and lacks tyrosine, tryptophan, and cysteine. The proteins from both strains show immunological identity with a similar DNA-binding protein from Escherichia coli, when tested by immunodiffusion with an antiserum prepared against the E. coli protein. Both the Aphanocapsa and E. coli proteins form compact, rapidly sedimenting complexes with cyanophage or bacteriophage DNA. The similarities between the proteins from cyanobacteria and E. coli suggest a degree of evolutionary conservation comparable to that of the histones of eukaryotes.
Responses of Phycomyces indicating optical excitation of the lowest triplet state of riboflavin.
Authors: Delbrück M , Katzir A , Presti D
Published: May 2006

Phototropic and light growth responses of the sporangiophore of Phycomyces have been elicited using tunable laser stimulation from 575 to 630 nm. The growth response shows additional components of the action spectrum with a sharp peak at 595 nm, a sharp cut-off at 585 nm, and a tail extending beyond 630 nm. The integral over the electronic transition (f-value) is 1.5 X 10(-9) times that at 455 nm. These parameters indicate a direct transition from the ground state to the lowest triplet state of riboflavin.
Sensitivity of calcium binding in cerebral tissue to weak environmental electric fields oscillating at low frequency.
Authors: Bawin S M , Adey W R
Published: May 2006

Weak sinusoidal electric fields modify the calcium efflux from freshly isolated chick and cat cerebral tissues bathed in Ringer's solution, at 36 degrees. Following incubation (30 min) with radioactive calcium (45Ca2+), each sample, immersed in fresh solution, was exposed for 20 min to fields at 1, 6, 16, 32, or 75 Hz, with electric gradients of 5, 10, 56, and 100 V/m in air. 45Ca2+ efflux in the solution was then measured in 0.2 ml aliquots and compared with efflux from unexposed control samples. Field exposures resulted in a general trend toward a reduction in the release of the preincubated 45Ca2+. Both frequency and amplitude sensitivities were observed. Maximum decreases occurred at 6 and 16 Hz (12-15%). Thresholds were around 10 and 56 V/m for chick and cat tissues, respectively. Similar but nonsignificant trends occurred during other field exposures. All results were statistically compared with matched samples of controls. Tissue gradients could not be measured, but estimates were of the order of 0.1 muV/cm. The susceptibility of the electrochemical equilibrium in the neuronal membrane to small extracellular perturbations is discussed and a possible role for weak intrinsic cerebral fields in neuronal excitability is suggested.
Biogenesis of mitochondria: molecular mapping of the mitochondrial genome of yeast.
Authors: Linnane A W , Lukins H B , Molloy P L , Nagley P , Rytka J , Sriprakash K S , Trembath M K
Published: May 2006

We have developed a new procedure for the detailed molecular mapping of any allele of the yeast (Saccharomyces cerevisiae) mitochondrial genome. The procedure employs a collection of different genetically characterized petite strains whose genomes have been physically defined by molecular hybridization. The map position of an allele is within the DNA segment common to all defined petites that can be shown by marker rescue to retain the locus. The same collection of petites can be used to locate the positions of mitochondrial rRNA and tRNA cistrons and DNA fragments produced by restriction endonucleases.