bluuebunny/crossref_metadata_2025 huggingface dataset:
Major histocompatibility complex-linked immune-responsiveness is acquired by lymphocytes of low-responder mice differentiating in thymus of high-responder mice.
Authors: von Boehmer H , Haas W , Jerne N K
Published: May 2006

Female murine T cells can respond to the Y antigen of male cells by generating cytotoxic T-killer lymphocytes. Responsiveness is linked to several H-2 genes. Two types of low responders can be distinguished: the B10.A(5R) (H-2i5) strain, a low responder because it lacks Y-specific precursor T cells able to differentiate into cytotoxic T-killer cells; and the CBA/J (H-2k) strain, a low responder because it lacks Y-specific T-helper cells able to support differentiation of T-killer cell precursors. B10.A(5R) stem cells differentiating in an x-irradiated (CBA/J X C57BL/6) (H-2k X H-2b)F1 host respond to Y antigen by generating T-killer cells whereas CBA/J stem cells do not. The results are consistent with the hypothesis that diversity of T-cell receptors is generated by somatic mutation of germ-line genes encoding specificity for self-H-2. A detailed account of this hypothesis is presented.
Terminal differentiation of human promyelocytic leukemia cells induced by dimethyl sulfoxide and other polar compounds.
Authors: Collins S J , Ruscetti F W , Gallagher R E , Gallo R C
Published: May 2006

A human leukemic cell line (designated HL-60) has recently been established from the peripheral blood leukocytes of a patient with acute promyelocytic leukemia. This cell line displays distinct morphological and histochemical commitment towards myeloid differentiation. The cultured cells are predominantly promyelocytes, but the addition of dimethyl sulfoxide to the culture induces them to differentiate into myelocytes, metamyelocytes, and banded and segmented neutrophils. All 150 clones developed from the HL-60 culture show similar morphological differentiation in the presence of dimethyl sulfoxide. Unlike the morphologically immature promyelocytes, the dimethyl sulfoxide-induced mature cells exhibit functional maturity as exemplified by phagocytic activity. A number of other compounds previously shown to induce erythroid differentiation of mouse erythroleukemia (Friend) cells can induce analogous maturation of the myeloid HL-60 cells. The marked similarity in behavior of HL-60 cells and Friend cells in the presence of these inducing agents suggests that similar molecular mechanisms are involved in the induction of differentiation of these human myeloid and murine erythroid leukemic cells.
Localization of acetylcholine receptor in excitable membrane from the electric organ of Torpedo: Evidence for exposure of receptor antigenic sites on both sides of the membrane.
Authors: Tarrab-Hazdai R , Geiger B , Fuchs S , Amsterdam A
Published: May 2006

Nicotinic acetylcholine receptor was localized in a receptor-rich membrane preparation from the electric organ of Torpedo californica by applying an immunoferritin technique. The membrane preparation was incubated with (Fab')2 fragments derived from specific rabbit antibodies against the purified acetylcholine receptor and subsequently with ferritin-conjugated goat antiserum to rabbit immunoglobulin. More than 50% of the vesicles were found to be labeled with ferritin while the rest remained unlabeled. Ferritin labeling on both sides of the membrane was evident in open membrane vesicles, whereas in closed vescles the labeling was confined to the outer surface due to the inability of the tracer to penetrate the membrane. These data suggest that antigenic sites of the receptor molecule are exposed on both sides of the excitable membrane, and that acetylcholine receptor may be a transmembrane protein.
Molecular mechanism of mitogen action: Processing of receptor induced by epidermal growth factor
Authors: Das Manjusri , Fox C. Fred
Published: May 2006

An affinity labeling technique used previously for identification of a membrane receptor for epidermal growth factor (EGF) was exploited to investigate the physiological fate of receptor after binding of EGF. Incubation of affinity-labeled cells at 37° resulted in a time-dependent loss of radioactivity from the EGF-receptor covalent complex (
M
r
190,000). Ninety percent of the radioactivity lost from the band of
M
r
190,000 during a 1-hr incubation at 37° appeared in three bands of
M
r
62,000, 47,000, and 37,000. The crosslinked EGF-receptor complex (
M
r
190,000) on intact cells was accessible to the action of trypsin at 4° and cofractionated with the plasmalemmal fraction. The proteolytic processing products of receptor were inaccessible to trypsin and banded with the lysosomal fraction upon subcellular fractionation. The rate of internalization and proteolytic processing of radiolabeled receptor was the same as the rate of reduction of binding activity induced by EGF. A study of the relationship between EGF-induced receptor internalization and processing, and stimulation of DNA synthesis, showed that both these processes were half-maximally stimulated at approximately 0.1 nM EGF, a concentration at which only 10% of the receptor sites are occupied. These data indicate that at concentrations of EGF subsaturating for binding but optimal for biological activity, there is a slow, continuous process of receptor internalization and degradation which could be limiting for EGF-induced mitogenesis.
Amino-terminal amino acid sequence of the major structural polypeptides of avian retroviruses: sequence homology between reticuloendotheliosis virus p30 and p30s of mammalian retroviruses.
Authors: Hunter E , Bhown A S , Bennett J C
Published: May 2006

The major structural polypeptides, p30 of reticuloendotheliosis virus (REV) (strain T) and p27 of avian sarcoma virus B77, have been compared with regard to amino acid composition. NH2-terminal amino acid sequence, and immunological crossreactions. The amino acid composition of the two polypeptides is distinct, and a comparison of the first 30 NH2-terminal amino acids of REV p30 with that for the first 25 of B77 p27 yields only three homologous residues. In competition radioimmunoassays the polypeptides show no crossreactivity. A comparison of the amino acid composition and NH2-terminal amino acid sequence of REV p30 with those reported for several mammalian retrovirus p30s shows remarkable similarities. Both REV and mammalian p30s contain a large number of polar residues in their amino acid composition and show approximately 40% homology in the first 30 NH2-terminal amino acids. No crossreactivity could be observed, however, in competition radioimmunoassays between Rauscher murine leukemia virus p30 and that of REV. The observations reported here suggest a close evolutionary relationship between REV and the mammalian retroviruses.
Mode of action of the hemin-controlled inhibitor of protein synthesis: studies with factors from rabbit reticulocytes.
Authors: de Haro C , Ochoa S
Published: May 2006

Previously [de Haro, C., Datta, A & Ochoa, S. (1978) Proc. Natl. Acad. Sci. USA 75, 243--247] it was shown with initiation factors from Artemia salina embryos that the activity of the initiator methionyl-tRNA binding factor eIF-2 is stimulated by another factor (ESP, for eIF-2 stimulating protein) present, like eIF-2, in ribosomal salt washes. Incubation of eIF-2 with translational inhibitor from rabit reticulocytes, in the presence of ATP, abolished the ESP effect. At physiological concentrations eIF-2 was virtually inactive without ESP. These observations indicated that the translational inhibitor acts by converting eIF-2 to a form that is not stimulated by ESP. The same observations have now been made with eIF-2 and ESP from rabbit reticulocytes but, in this case, the dependence of eIF-2 activity on ESP is much more pronounced than with the A. salina factors. eIF-2 from reticulocytes interacts with ESP from A. salina and conversely.
Assay for early cytoplasmic effects of the
src
gene product of Rous sarcoma virus
Authors: McClain Donald A. , Maness Patricia F. , Edelman Gerald M.
Published: May 2006

When microinjected into normal fibroblasts, cytoplasmic extracts of cells transformed by Rous sarcoma virus caused dissolution of microfilament bundles. This activity was not found in extracts of normal cells. The maximum effect was seen within 30 min of injection, and the activity could still be measured after a 10-fold dilution of the cytoplasmic extracts (14 mg/ml original protein concentration). The activity was trypsin sensitive and was destroyed by boiling, but was not RNase sensitive. Protein synthesis was not required for the disruption of actin-containing stress fibers by the injected activity. Microinjected cytoplasts prepared from normal 3T3 cells also showed dissolution of microfilament bundles, indicating that the cell nucleus was not required for expression of activity. Extracts made from fibroblasts transformed by Rous sarcoma virus having a temperature-sensitive mutation in the
src
gene were also temperature sensitive in the microinjection assay. Thus, the activity of extracts from cells infected with
src
mutant virus, but not from cells infected with wild-type virus, was destroyed either by
in vitro
incubation of the extract at the nonpermissive temperature before injection or by incubation of recipient cells at the nonpermissive temperature after injection.

We conclude that the microinjection assay can detect a cytoplasmic activity coded for by the
src
gene of Rous sarcoma virus and that an early direct or indirect target of the
src
gene product is the cytoskeleton and cell motility system. This result is discussed in relation to the hypothesis that submembranous arrays of microfilaments, microtubules, and their associated proteins interact with cell surface receptors to form a surface modulating assembly that functions as a key regulator of cell growth.
Regulation of the galactose pathway in
Saccharomyces cerevisiae
: Induction of uridyl transferase mRNA and dependency on
GAL4
gene function
Authors: Hopper James E. , Broach James R. , Rowe Lucy B.
Published: May 2006

In
Saccharomyces cerevisiae
, utilization of galactose requires four inducible enzyme activities. Three of these activities (galactose-1-phosphate uridyl transferase, EC 2.7.7.10; uridine diphosphogalactose 4-epimerase, EC 5.1.3.2; and galactokinase, EC 2.7.1.6) are specified by three tightly linked genes (
GAL7, GAL10
, and
GAL1
, respectively) on chromosome II, whereas the fourth, galactose transport, is specified by a gene (
GAL2
) located on chromosome XII. Although classic genetic analysis has revealed both positive and negative regulatory genes that coordinately affect the appearance of all four enzyme activities, neither the basic events leading to the appearance of enzyme activities nor the roles of the regulatory genes have yet been determined. Regulation of inducible enzyme activity could be mediated by events related to transcription, translation, or enzyme activation. For the purpose of studying galactose pathway induction and its regulation, we have developed an immunoprecipitation assay that enables us to detect the
GAL7
specified uridyl transferase polypeptide in yeast extracts and among the polypeptides synthesized in an RNA-dependent
in vitro
translation system. Use of this immunoprecipitation assay in conjunction with
in vivo
labeling experiments demonstrates the presence of [
3
H]leucine-labeled transferase in extracts prepared from cells grown in galactose but not from cells grown in glucose. This galactose-specific induction of transferase polypeptide is mediated by the
de novo
appearance of a functional mRNA species whose synthetic capacity is detectable by the combination of
in vitro
translation and immunoprecipitation. The appearance of functional transferase mRNA depends on wild-type expression of the positive regulatory gene,
GAL4
. Cells carrying a nonsense (amber) mutation in the
GAL4
gene fail to produce the transferase mRNA, whereas a nonsense suppressor of the
GAL4
amber mutant regains the galactose-specific mRNA response. Our results establish that the induction of the
GAL7
specified uridyl transferase activity is mediated by
de novo
appearance of a functional mRNA and that this galactose-specific response is dependent on a wild-type
GAL4
gene product.
Hormonal induction of the secretory immune system in the mammary gland.
Authors: Weisz-Carrington P , Roux M E , McWilliams M , Phillips-Quagliata J M , Lamm M E
Published: May 2006

The secretory immune system of the mammary gland is undeveloped in virgin mice but becomes active at term and during lactation. This change appears to depend on migration to the mammary gland of precursors of IgA-secreting cells derived from the gut-associated lymphoid tissue, an origin which explains the specificity of milk IgA antibodies for enteric organisms. Because development of the epithelial components of the mammary gland is clearly under hormonal control, we examined the effect of mammotropic hormones on differentiation of the immune elements. Under a combined regimen of progesterone, estrogen, and prolactin, development of the glandular epithelium occurs with concomitant increments in the number of IgA-secreting plasma cells and amount of intraepithelial IgA. These increases appear to be due to enhanced capacity of the gland to attract or retain precursors of IgA plasma cells derived from gut-associated lymphoid tissue. Testosterone, which antagonizes lactation, also antagonizes development of the secretory immune system and decreases cellular trapping in the lactating gland. The ability of the gland to trap IgA immunoblasts is probably contingent upon a hormone-induced increase in receptors.
Cell fusion induced by scrapie and Creutzfeldt-Jakob virus-infected brain preparations.
Authors: Kidson C , Moreau M C , Asher D M , Brown P W , Coon H G , Gajdusek D C , Gibbs C J
Published: May 2006

Cell fusion was induced by brain extracts containing the scrapie virus and the virus of Creutzfeldt-Jakob disease. The assay involved quantitation of colony-forming ability in a double selection system, strandardized against fusion induced by Sendai virus. Correlation between the logarithm of virus dilution and the hybrid colony number gave similar curves for scrapie virus and Sendai virus. Fusion induction may explain some aspects of pathogenesis in these diseases and provide a potential in vitro assay.
Interacting enzyme systems at steady state: location of the phase transition in approximations of the mean field type.
Authors: Hill T L , Chen Y D
Published: May 2006

We consider a phase transition "loop," obtained from a mean field type of approximate treatment of a closed steady-state Ising system. Where is the cut (stable path) across the loop located? The general procedure, in answering this question, is to pass to an open version of the same system and use the cut that appears automatically in this case (no loop is possible in an open system). This is equivalent to finding the point at which the two phases have equal total probability in the open system. It is shown here that this procedure, when applied to a system of two-state enzyme molecules, is formally equivalent to well-known thermodynamic methods (Maxwell's theorem, etc.). These can be applied directly to the closed system without considering the open system explicitly. However, for enzyme molecules with more than two states, the "thermodynamic" method generally fails and one must fall back on the open system procedure mentioned above. Practical implementation of this procedure is not easy.
Maxwell-type constructions for multiple nonequilibrium steady states
Authors: Keizer Joel
Published: May 2006

A stochastic analysis is used to obtain Maxwell-type constructions for multiple nonequilibrium steady states in homogeneous systems. The stochastic theory shows that homogeneous molecular fluctuations can nucleate the Maxwell construction only on a time scale that is the order of a Poincaré recurrence time and indicates that hysteresis should be observed. The nonrelevance of homogeneous fluctuations for systems that undergo phase separation or in which spatial structures occur is discussed.
Structural characterization of H-2 antigens purified from mouse liver.
Authors: Henriksen O , Robinson E A , Appella E
Published: May 2006

Papain solubilized H-2a histocompatibility antigens (H-2Kk plus H-2Dd) have been purified by a large-scale procedure that can routinely provide 2-3 mg of heavy chain from 1 kg of mouse liver. The heavy chains were homogeneous by sodium dodecyl sulfate electrophoresis. Disc gel electrophoresis resolved two protein bands that were identified as H-2Dd and H-2Kd by immune complex formation and autoradiography. Comparative amino acid composition and NH2-terminal sequence analyses of unfractionated H-2a, H-2Kk, and HLA suggested close structural relationships. However, the following observations suggest that papain cleaves these membrane bound antigens at different positions with respect to the COOH terminus: the molecular weight of the peptide portion of papain solubilized HLA is smaller than that of H-2 (30,000 versus 33,700); the COOH-terminal sequences are different; and, finally, papain-solubilized H-2 contains a free cysteine residue in addition to the two disulfide bridges that are present in both H-2 and HLA.
Biochemical evidence for a deficiency of vitamin B
6
in the carpal tunnel syndrome based on a crossover clinical study
Authors: Folkers Karl , Ellis John , Watanabe Tatsuo , Saji Seisuke , Kaji Masahiro
Published: May 2006

In a patient with severe carpal tunnel syndrome and a significant deficiency of vitamin B
6
, the evidence for the deficiency was an extraordinarily low basal specific activity of the glutamic-oxaloacetic transminase of the erythrocytes (EGOT). This enzyme was also deficient in pyridoxal phosphate. The patient was treated with the recommended dietary allowance of pyridoxine, 2 mg/day, for 11 weeks, then 100 mg/day for 12 weeks, a placebo for 9 weeks, and again pyridoxine at 100 mg/day for 11 weeks. Sixty-one monitorial assays of EGOT over 48 weeks supported the following interpretations. (
i
) His diet permitted the development of a debilitating carpal tunnel syndrome. (
ii
) Treatment with pyridoxine at 2 mg/day reduced the deficiency of EGOT activity from about 70% to 50%, maintained a deficiency of pyridoxal phosphate, and relieved but allowed a marginal syndrome. (
iii
) Treatment at 100 mg/day for 12 weeks nearly achieved a “ceiling” level of EGOT and eliminated the deficiency of pyridoxal phosphate. (
iv
) After placebo for 7 weeks, the deficiencies of EGOT activity and pyridoxal phosphate reappeared, and clinical symptoms become worse. (
v
) Retreatment at 100 mg/day reestablished a “ceiling” EGOT, with no deficiency of pyridoxal phosphate, and the patient was asymptomatic. These data also support the concept that a deficiency of vitamin B
6
is significant in the etiology of the carpal tunnel syndrome. Mechanistically, a state of deficiency of the coenzyme seems to lower the level of the apoenzyme; a state of no deficiency of the coenzyme regulates a ceiling level of the transaminase. The latter state is presumably desired for health.
Coronary vasodilator activity of 13,14-dehydroprostacyclin methyl ester: comparison with prostacyclin and other prostanoids.
Authors: Hyman A L , Kadowtiz P J , Lands W E , Crawford C G , Fried J , Barton J
Published: May 2006

The effects of a recently synthesized, stable prostacyclin (PGI2) analog, 13,14-dehydro-PGI2 methyl ester, and authentic PGI2 and several other prostanoids on the coronary circulation were investigated in the intact dog by using a new technique to measure coronary sinus blood flow. The PGI2 analog, PGI2, and prostaglandin (PG) E2 and D2 each increased coronary sinus blood flow in a dose-related fashion when injected into the left coronary artery. The analog and PGE2 had similar vasodilator activity while PGI2 was slightly more potent. PGD2 was a moderately active coronary vasodilator whereas PGF2alpha was inactive. The coronary vasodilator effects of PGI2, its analog, PGE2, and PGD2 occurred at doses that had little effect on aortic pressure, left ventricular pressure and its first derivative, or on cardiac output and heart rate. The prostaglandin precursor arachidonic acid and the endoperoxide intermediate PGH2 both increased coronary sinus blood flow in a dose-dependent manner. The effects of arachidonic acid were inhibited by indomethacin. These data show that PGE2, PGI2, and a stable PGI2 analog are potent vasodilators in the canine coronary vascular bed and suggest that the vasodilator effects of arachidonic acid and PGH2 may be due to the formation of PGE2, PGD2, or PGI2 in the dog heart.
Nearest-neighbor interactions of the major RNA tumor virus glycoprotein on murine cell surfaces.
Authors: Takemoto L J , Fox C F , Jensen F C , Elder J H , Lerner R A
Published: May 2006

Formaldehyde-fixed Staphylococcus aureus and monospecific antiserum to gp70, the major envelope glycoprotein of murine leukemia virus, were used to immunoadsorb gp70 from Nonidet P40 extracts prepared from surface-radioiodinated murine cells. The labeled gp70 molecules in these cells were linked to a protein of approximately 15,000 daltons via native disulfide bonding. Prior treatment of cells with the reversible, bifunctional, crosslinking reagent dimethyl-3,3'-dithiobispropionimidate, followed by immunoadsorption and two-dimensional diagonal electrophoresis, revealed apparent homodimers and homotrimers of the 85,000-dalton complex. Identical treatment of purified type C RNA tumor virus from murine cells also revealed homodimeric and homotrimeric species, demonstrating similar self-associating tendencies of this glycoprotein in both intact virus and the plasma membrane of nonproducing murine cells. One cross-linked product consistently detected on the surfaces of murine cells was not present after crosslinking of a representative strain of murine leukemia virus.
High-resolution 13C nuclear magnetic resonance studies of glucose metabolism in Escherichia coli.
Authors: Ugurbil K , Brown T R , den Hollander J A , Glynn P , Shulman R G
Published: May 2006

High-resolution 13C nuclear magnetic resonance spectra of suspensions of Escherichia coli cells have been obtained at 90.5 MHz by using the Fourier transform mode. Anaerobic cells incubated with [I-13C]glucose show a time course of glycolysis in which the alpha and beta glucose anomers disappear at different rates, lactate, succinate, acetate, alanine, and valine accumulate as end products of glycolysis, and fructose bisphosphate appears as an intermediate. It is shown that fructose bisphosphate is labeled at C-1 and C-6 during [I-13C]-glucose catabolism. Upon oxygenation, glutamate appears with the 13C ENRICHMENT AT THE C-4, C-3, and C-2 positions, with the C-4 most intense. From the position of the 13C label we conclude that valine is formed by condensation of pyruvate and that carbon enters the tricarboxylic acid cycle mainly through acetyl CoA.
Post-transcriptional suppression of globin gene expression in cells transformed by avian erythroblastosis virus.
Authors: Therwath A , Scherrer K
Published: May 2006

Cells transformed by avian erythroblastosis virus were grown in vitro for up to 5 months. After a few days in culture, synthesis of hemoglobin was undetectable and could not be induced by dimethyl sulfoxide. As shown by globin cDNA hybridization to nuclear and cytoplasmic RNA carried to Crot values of 10(5) moles of nucleotide per liter X sec, globin genes in these cells are transcribed into pre-mRNA, but no trace of globin mRNA appears in the cytoplasm. The implications of this observation for schemes of post-transcriptional regulations and viral transformation are discussed.
Uridine diphosphate N-acetylglucosamine stimulates uptake of nutrients by quiescent BALB/C3T3 cells.
Authors: Natraj C V , Datta P
Published: May 2006

Preincubation of quiescent BALB/C3T3 cells with uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) in conditioned medium resulted in a time- and concentration-dependent stimulation of uptake of 2-deoxyglucose, uridine, and alpha-aminoisobutyric acid over that seen in conditioned medium alone. The apparent Km values for 2-deoxyglucose and uridine uptake were the same for cells incubated with or without UDP-GlcNAc, whereas the Vmax values were higher for cells pretreated with the nucleotide sugar. The stimulation of uptake was specific for UDP-GlcNAc, and the other nucleotide sugars tested were ineffective; incubation of UDP-GlcNAc-pretreated cells with N-acetylglucosaminidase abolished the stimulatory effect. In all cases, the extent of stimulation of nutrient uptake was comparable to that seen with serum-stimulated cells. Incubation of quiescent cells in situ with UDP-[3H]GlcNAc led to incorporation of radioactive N-acetylglucosamine into the acid-precipitable fraction; a large fraction of the labeled amino sugar was found on the cell surface acceptors. We interpret these data to mean that the cellular acceptors of quiescent cells are "under-glycosylated," at least in terms of N-acetylglucosamine, and that stimulation of uptake of nutrients may be a consequence of restoration of the amino sugar residues on the oligosaccharide chains of acceptors on the cell surface.
Isolation of myeloma variants with predefined variant surface immunoglobulin by cell sorting.
Authors: Liesegang B , Radbruch A , Rajewsky K
Published: May 2006

We describe a procedure for the isolation of somatic cell variants in which gene products are expressed on the cell surface that are not expressed in the wild type. Cloned cells of the myeloma line MPC 11, which expresses an IgG2b protein, were incubated with an antiserum specific for IgGI and IgG2a. Cells reacting with this antiserum were stained with a fluorescent anti-antiserum and enriched in three cycles of sorting in the fluorescence-activated cell sorter and subsequent growth in vitro. From the enriched population two variants were isolated by cloning in soft agar. One of them expressed a variant immunoglobulin that types serologically as an IgG2a but whose variable portion was idiotypically related to that of the MPC 11 wild-type protein.
A factor from neurons increases the number of acetylcholine receptor aggregates on cultured muscle cells.
Authors: Christian C N , Daniels M P , Sugiyama H , Vogel Z , Jacques L , Nelson P G
Published: May 2006

There is an increase in the number of acetylcholine (AcCho) receptor aggregates on striated embryonic mouse myotubules when they are cocultured with clonal neuroblastoma-glioma hybrid cells. Medium conditioned by hybrid cells contains a factor which increases the number of AcCho receptor aggregates on myotubes cultured from mouse, rat or chick muscle. AcCho receptor-aggregating activity was present in medium conditioned by the neuroblastoma parent clone but was not detected in medium conditioned by cells of the parent glioma clone, fibroblasts, or HeLa cells. The factor increased the aggregation of AcCho receptors within 24 hr without a significant increase in the total number of AcCho receptors, and its action did not depend on myotube protein synthesis. The factor appears to rearrange the distribution of myotube AcCho receptors either by aggregating mobile AcCho receptors or by stabilizing labile receptor aggregates.
Detection of unique tRNA species in tumor tissues by Escherichia coli guanine insertion enzyme.
Authors: Okada N , Shindo-Okada N , Sato S , Itoh Y H , Oda K , Nishimura S
Published: May 2006

The guanine insertion enzyme from Escherichia coli catalyzes exchange of guanine located at the first position of the anticodon of tRNA with radioactive guanine (N. Okada and S. Nishimura, unpublished data). tRNA isolated from various tumors, including slowly growing Morris hepatoma 7794A, incorporated considerable guanine with E. coli guanine insertion enzyme, whereas tRNA isolated from all normal tissues so far tested, except regenerating rat liver, incorporated scarcely any. In the rat ascites hepatoma AH7974, the guanine was mostly incorporated into minor isoaccepting species of tRNAAsp that contained the guanine residue instead of Q base in the first position of the anticodon. This is a sensitive and easy method for identifying unique tRNA species in tumor tissues.
Isolation of methylglyoxal from liver.
Authors: Fodor G , Mujumdar R , Szent-Gyorgyi A
Published: May 2006

Acetaldehyde and methylglyoxal were shown to be present in liver bound to protein. They were isolated in the form of 2,4-dinitrophenylhydrazones and osazones, respectively. The NMR spectrum of pure methylglyoxal was recorded.
Modulation of macrophage tumoricidal capability by polyene antibiotics: support for membrane lipid as a regulatory determinant of macrophage function.
Authors: Chapman H A , Hibbs J B
Published: May 2006

We have examined the effects of the sterol-binding polyene antibiotics on macrophage tumoricidal capability. Incubation for 2 hr of activated macrophages from bacillus Calmette-Guérin-infected mice with amphotericin B at 0.5--2 microgram/ml or amphotericin B methyl ester at 0.5--10 microgram/ml enhanced the capability of activated macrophages to kill 3T12 cells. These polyenes did not make normal or stimulated macrophages tumoricidal. Experiments with the ionophores gramicidin, alamethecin, nigericin, and valinomycin indicate that the ionophoretic properties of amphotericin B may not account for its enhancing effect on macrophage tumoricidal potential. Two polyenes with a smaller ring structure, filipin and pimaricin, were also ineffective suggesting that stereospecific modifications in membrane lipid organization underlie the enhancing effect of amphotericin B. The results suggest that the clinical efficacy of amphotericin B in promoting resistance to fungal disease and possibly to neoplasia may operate in part through potentiation of macrophage effector functions.
Regulation of corneal collagenase production: epithelial-stromal cell interactions.
Authors: Johnson-Muller B , Gross J
Published: May 2006

Mixtures of epithelial and stromal cells isolated from normal adult rabbit cornea, when cocultured in the presence of cytochalasin B, produced latent collagenase, whereas neither cell type alone, nor the mixture in the absence of this agent, did so. The enzyme, a characteristic animal collagenase, required proteolytic activation. The relative concentrations of epithelial and stromal cells had a profound effect on on collagenase production, the enzyme activity bieng directly proportional to the number of stromal cells but inversely proportional to the number of epithelial cells. The amount of enzyme released into the medium was also directly proportional to cytochalasin B concentration. Media conditioned by cytochalasin B-treated epithelial or stromal cells did not stimulate collagenase secretion by the other cell type. The data suggest direct cell contact or close proximity as the mode of productive interaction and tentatively identify the stromal cell as the source of enzyme and the epithelial cell as a stimulator.
Actin may be present on the lymphocyte surface.
Authors: Owen M J , Auger J , Barber B H , Edwards A J , Walsh F S , Crumpton M J
Published: May 2006

Lymphocytes were assessed for the presence of surface actin and myosin by lactoperoxidase-catalyzed iodination and indirect immunofluorescence using antisera against purified pig skeletal muscle actin and pig smooth muscle myosin. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of 125I-labeled pig, mouse, and human B lymphocytes revealed an intense radioactive band of 43,000 molecular weight, whereas pig and mouse T lymphocytes gave a much less intense band. This band comigrated with actin, was nonglycosylated as judged by lack of binding to lentil lectin-Sepharose, was bound specifically by myosin fibers, and could be distinguished from a polypeptide of similar mobility derived from the major histocompatibility antigens. These results suggest that actin is present on the surface of B lymphocytes and, to a lesser extent, on T lymphocytes. Pig, mouse, and human Ig-bearing cells were stained by antiactin and antimyosin antisera, as judged by indirect immunofluorescence, whereas non-Ig-bearing cells were not stained. Antibody binding, however, was depleted by adsorbing the antisera with Ig-Sepharose. It was concluded that the immunofluorescence results are misleading and reflect the presence of antibodies that crossreact with Ig.
Isolated microvessels: the blood-brain barrier in vitro.
Authors: Hjelle J T , Baird-Lambert J , Cardinale G , Specor S , Udenfriend S
Published: May 2006

Isolated bovine retinal and brain microvessels, exhibiting a patent lumen, were used to study the contribution of the microvasculature to the blood-brain and blood-retina barriers. The diffusion marker, sucrose, was taken up slowly by the isolated microvessels in contrast to leucine, tyrosine, and valine which were taken up at a considerably faster rate. Uptake of leucine was temperature dependent but resistant to inhibition by ouabain and sodium azide. The large neutral amino acids exhibited stereospecificity and cross-competition for uptake by the isolated microvessels. The apparent Kms for uptake for tyrosine, leucine, and valine were III micron,133 micron, and 500 micron, respectively.
Nerve growth factor-mediated induction of tyrosine hydroxylase in a clonal pheochromocytoma cell line.
Authors: Goodman R , Herschman H R
Published: May 2006

We have established a clonal cell line, PC-G2, from an experimentally induced rat pheochromocytoma. Administration of nerve growth factor to PC-G2 causes a 4- to 8-fold induction in the specific activity of tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine,tetrahydropteridine:oxygen oxidoreductase(3-hydroxylating); EC 1.14.16.2]. The response is elicited in a dose-dependent fashion, at concentrations above 0.1 microgram/ml. Antiserum to nerve growth factor inhibited the induction of tyrosine hydroxylase. Dexamethasone enhances the nerve growth factor-mediated elevation of tyrosine hydroxylase. After 3--4 days of exposure to nerve growth factor the maximal induction of tyrosine hydroxylase is seen, although a significant increase can be observed after 24 hr. In contrast to the PC-12 cell line (derived from the same tumor), in which neurite outgrowth occurs in response to nerve growth factor, there is no morphological change or alteration in growth rate of PC-G2 cells after exposure to nerve growth factor.
Translational and post-translational cleavage of M13 procoat protein: extracts of both the cytoplasmic and outer membranes of Escherichia coli contain leader peptidase activity.
Authors: Mandel G , Wickner W
Published: May 2006

The coat protein of coliphage M13 is an integral protein of the host cytoplasmic membrane at all stages of the infectious cycle. Both in in vivo and DNA-directed in vitro synthesis, it is initially made with an NH2-terminal "leader peptide" of 23 amino acids and is termed procoat. We now report that leader peptidase, and activity which removes the leader peptide and converts procoat to coat, is found in both the inner (cytoplasmic) and outer membrane of Escherichia coli. However, only cytoplasmic membranes will catalyze cleavage of procoat in the absence of detergent. Leader peptidase will cleave procoat either during translation or after protein synthesis is complete.
Identification of a methyl-accepting chemotaxis protein for the ribose and galactose chemoreceptors of Escherichia coli.
Authors: Kondoh H , Ball C B , Adler J
Published: May 2006

The ribose and galactose chemoreceptors of Escherichia coli have previously been identified as the ribose- and galactose-binding proteins. We now report the discovery of a methyl-accepting chemotaxis protein that functions in the transfer of receptor signals from these two binding proteins to the flagella. This protein is distinct from previously described methyl-accepting chemotaxis proteins. Its level of methylation is influenced by D-ribose, D-galactose, and certain structural analogues of them. This methyl-accepting protein is required for chemotaxis toward those attractants; mutants in the trg gene, which do not methylate this protein, are devoid of taxis toward D-ribose, D-galactose, and their analogues. In addition, methylation of the methyl-accepting protein in response to each of these attractants requires the appropriate binding protein. The binding protein's chemoreceptor function is required for such methylation, but its transport activity is not. Because the function of this methyl-accepting chemotaxis protein involves two of the best-characterized chemoreceptors, the discovery of this protein represents a promising base for further study of the linkage between chemoreceptors and flagella in bacteria.
Self-assembly of microtubules in extracts of cultured HeLa cells and the identification of HeLa microtubule-associated proteins.
Authors: Bulinski J C , Borisy G G
Published: May 2006

Microtubule protein from HeLa cell extracts was purified by multiple cycles of polymerization and depolymerization in the absence of glycerol or other exogenous polymerization-stimulatory agents. Approximately 4-5% of the extract protein was tubulin, of which more than one-half was competent to participate in polymerization-depolymerization cycles. The purified HeLa microtubule protein preparations contained 95% tubulin after the second cycle of polymerization and depolymerization. Additional protein species bound specifically to and copurified quantitatively with microtubules throughout at least four cycles of polymerization and depolymerization. These microtubule-associated proteins (MAPs) were separated from tubulin by DEAE column chromatography. When added to purified brain or HeLa tubulin, these MAPs stimulated the polymerization of microtubules as assayed by electron microscopy and a quantitative sedimentation assay. The most prominent HeLa MAPs had molecular weights of approximately 210,000 and 120,000.
Antibodies from patients with myasthenia gravis recognize determinants unique to extrajunctional acetylcholine receptors.
Authors: Weinberg C B , Hall Z W
Published: May 2006

We have examined the interaction between sera from patients with myasthenia gravis and acetylcholine receptor (AcChoR) purified from normal and denervated rat skeletal muscles [junctional receptor (JR) and extrajunctional receptor (EJR), respectively]. Eight of ten myasthenic sera had titers against EJR that were significantly higher (1.1-2.4 times) than their titers against JR. The antireceptor titers of these sera ranged from 2 to 102 nM. Although activities of three other sera were too low (less than 1 nM) to allow accurate titrations, provisional measurements with these sera gave titers against EJR that were at least as high (1.0-1.4 times) as those against JR. Competition experiments with myasthenic sera demonstrated two classes of determinants on rat AcChoR: those that are common to JR and EJR and those that are present or exposed only on EJR. Myasthenic sera did not recognize any determinants unique to JR. Several antisera raised to purified AcChoR from eel or Torpedo electric organs or denervated rat skeletal muscle had equal titers against the two forms of receptor. Treatment of JR and EJR by various enzymatic or chemical procedures designed to alter prosthetic groups on the proteins failed to affect their antigenic reactivity. AcChoR from embryonic rats was indistinguishable immunologically from EJR of adult muscle.
Subnanosecond motions of tryptophan residues in proteins
Authors: Munro Ian , Pecht Israel , Stryer Lubert
Published: May 2006

The dynamics of protein molecules in the subnanosecond and nanosecond time range were investigated by time-resolved fluorescence polarization spectroscopy. Synchrotron radiation from a storage ring was used as a pulsed light source to excite the single tryptophan residue in a series of proteins. The full width at half maximum of the detected light pulse was 0.65 nsec, making it feasible to measure emission anisotropy kinetics in the subnanosecond time range and thereby to resolve internal rotational motions. The proteins investigated exhibit different degrees of rotational freedom of their tryptophan residue, ranging from almost no mobility to nearly complete freedom in the subnanosecond time range. The tryptophan residue of
Staphylococcus aureus
nuclease B (20,000 daltons) has a single rotational correlation time (ϕ) of 9.9 nsec at 20°C, corresponding to a rotation of the whole protein molecule. By contrast, bovine basic A1 myelin protein (18,000 daltons) exhibits ϕ of 0.09 and 1.26 nsec, showing that the tryptophan residue in this protein is highly flexible. The single tryptophan of human serum albumin (69,000 daltons) has almost no rotational freedom at 8°C (ϕ = 31.4 nsec), whereas at 43°C it rotates rapidly (ϕ
1
= 0.14 nsec) within a cone of semiangle 26° in addition to rotating together with the whole protein (ϕ
2
= 14 nsec). Of particular interest in the large angular range (semiangle, 34°) and fast rate (ϕ
1
= 0.51 nsec) of the rotational motion of the tryptophan residue in
Pseudomonas aeruginosa
azurin (14,000 daltons). This residue is known to be located in the hydrophobic interior of the protein. The observed amplitudes and rates of these internal motions of tryptophan residues suggest that elementary steps in functionally significant conformational changes may take place in the subnanosecond time range.
The boundary value problem for maximal hypersurfaces
Authors: Flaherty F. J.
Published: May 2006

A spacelike hypersurface (condimension 1) in a Lorentzian manifold is called a maximal surface if it extremizes the hypervolume functional. Although maximal surfaces are superficially analogous to minimal hypersurfaces in Riemannian geometry, their properties can be dramatically different, as can be seen from the validity of Bernstein's theorem in all dimensions [Cheng, S.-Y. & Yau, S.-T. (1976)
Ann. Math.
104, 407-419]. Here we establish a point of contact between maximal surfaces and minimal surfaces by solving the Dirichlet problem for acausal boundary data but using boundary curvature conditions similar to those of H. Jenkins and J. Serrin [(1968)
J. Reine Angew. Math.
229, 170-187].
Sequences of vesicular stomatitis virus RNA in the region coding for leader RNA, N protein mRNA, and their junction.
Authors: Rowlands D J
Published: May 2006

The RNAs extracted from purified preparations of the Indiana and New Jersey serotypes of vesicular stomatitis virus were polyadenylylated in vitro by using polynucleotide phosphorylase and sequence determination was carried out by the dideoxynucleotide method using reverse transcriptase and dT8AC primer. On both virus RNAs a short stretch of adenylic acid residues is present between the regions coding for the leader and N protein mRNAs. Other features of the RNA sequences of the two viruses are compared to each other and to published data.
Comparison of bovine and mouse pituitary glycoprotein hormone pre-α subunits synthesized
in vitro
Authors: Giudice Linda C. , Waxdal Myron J. , Weintraub Bruce D.
Published: May 2006

Poly(A)-containing RNA isolated from bovine and mouse pituitaries and a mouse pituitary thyrotropic tumor was translated in a wheat germ cell-free biosynthetic system. A precursor of the glycoprotein hormone α subunit, “pre-α,” was immunoprecipitated from the translation mixtures with antiserum against bovine luteinizing hormone (LH; lutropin) α. The specificity of the immunoprecipitation was shown by competition with authentic bovine LHα and lack of competition with bovine thyroid-stimulating hormone (TSH; thyrotropin) β. Bovine and mouse pre-α subunits migrated identically in sodium dodecyl sulfate gradient polyacrylamide slab gels with an apparent molecular weight of about 17,000. Pre-α comprised 2-3% and 20-30% of the total proteins translated with pituitary and pituitary tumor mRNA, respectively. Microanalysis of amino acid sequence of the pre-α subunits containing various radiolabeled amino acids gave the following partial sequence for mouse tumor pre-α: [Formula: see text] Met was also found in positions 1, 14, and 17 in mouse pituitary pre-α but only in residue 1 of the bovine pituitary pre-α subunit. Leu was found in identical positions in bovine pituitary pre-α, with an additional Leu in position 17. Leu in the common positions (12, 15, 19, and 22) has also been found in human choriogonadotropin pre-α subunit [Birken, S., Fetherston, J., Desmond, J., Canfield, R. & Boime, I. (1978)
Biochem. Biophys. Res. Commun.
85, 1247-1253]. The data demonstrate that pituitary as well as placental glycoprotein hormone α subunits are synthesized with an amino-terminal hydrophobic extension, in accord with the “signal hypothesis” for secreted proteins. Furthermore, the positions of the hydrophobic amino acid Leu have been strictly conserved in pre-α subunits from various species and in two different tissues, the pituitary and placenta.
Translation and characterization of messenger RNAs in differentiating chicken cartilage.
Authors: Upholt W B , Vertel B M , Dorfman A
Published: May 2006

Total RNA, prepared from chicken limb bud cultures undergoing differentiation to cartilage, has been translated in a wheat germ cell-free protein-synthesizing system. Antibodies against chondroitin sulfate proteoglycan core protein immunoprecipitate a single component which migrates as a protein of 340,000 daltons in sodium dodecyl sulfate/polyacrylamide gels. The messenger RNA for this protein sediments at approximately 27 S in 70% formamide or aqueous sucrose gradients. The 340,000-dalton protein is present in cell-free translation products directed by RNA prepared from limb bud cultures and sternae and is absent in cell-free translation directed by RNA prepared from embryonic calvaria or liver. The level of synthesis of this protein is greatly reduced when RNA prepared from limb bud cultures inhibited from differentiation by BrdUrd is used. (Pre)pro alpha 1(I), -alpha 2(I), and -alpha 1(II) collagen bands have been identified on gels by electrophoresis of collagenase-digested or immunoprecipitated cell-free translation products directed by RNA from differentiating limb bud cultures, embryonic sternae, and embryonic calvaria.
Rate limitation of (Na+ + K+)-stimulated adenosinetriphosphatase by membrane acyl chain ordering.
Authors: Sinensky M , Pinkerton F , Sutherland E , Simon F R
Published: May 2006

A somatic cell mutant (CR1) of the Chinese hamster ovary cell line (CHO-K1) that is defective in the regulation of cholesterol biosynthesis can be grown under conditions in which plasma membranes from these cells display various cholesterol contents and acyl chain order parameters. The (Na+ + K+)-stimulated adenosinetriphosphatase (ATP phosphohydrolase, EC 3.6.1.3) from these cells was shown to vary in activity by a factor of 10 as the order parameter was varied, and the activity exhibited an exponential dependence on this parameter. Under these conditions the number of Na+,K+-ATPase molecules was shown to remain constant by affinity labeling with [gamma-32P]ATP in the absence of Na+. Control experiments showed that alteration in cholesterol content without change in order parameter did not result in altered enzyme activity. It is concluded that, under our conditions, the rate of catalysis by the Na+,K+-ATPase is determined by the order parameter. These studies suggest a physical mechanism by which variation of membrane lipid composition or other factors that determine membrane lipid acyl chain order parameter can result in variation in membrane enzyme activity.