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Biomedical subjects

V G Allfrey

Publications and source records attributed to V G Allfrey.

At least 73 records · Page 4Linked to original sources
PubMed1978

Inhibition of mammalian protein kinase and phosphodiesterase activities by a cyclic AMP-like compound isolated from higher plants.

A cyclic AMP-like substance has been isolated from higher plant tissues which can be quantitated with the use of a radioimmunoassay similar to that described by A. L. Steiner, D. M. Kipnis, R. Utiger, and C. Parker [(1969) Proc. Natl. Acad. Sci. USA 64, 367-373]. This compound has been extensively purified and is chromatographically distinct from authentic cyclic AMP. This cyclic AMP-like compound inhibited beef heart 3':5'-cyclic-nucleotide phosphodietsterase (3':5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17), with half-maximal inhibition occurring at a concentration of 7.6 X 10(-10) M cyclic AMP equivalents. The compound also inhibited cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase; EC 2.7.1.37) from bovine heart, with half-maximal inhibition of mixed histone phosphorylation occurring at 8.0 X 10(-11) M cyclic AMP equivalents. Equipotent inhibition of phosphorylation and associated trace ATPase activity were observed with the purified catalytic subunit of cyclic AMP-dependent protein kinase from calf thymus with a synthetic heptapeptide as substrate. Moreover, steady-state kinetic analysis of this inhibition in the latter system showed it to be nonlinear and noncompetitive versus MgATP.

Adenosine Triphosphatases↗
PubMed1977

Overview: molecular changes associated with large bowel cancer and their potential as markers and chemotherapeutic agents.

The search for molecular changes that may be diagnostic of malignancy in the colonic epithelium is complicated by the diversity of cell types and complex cell kinetics of a tissue in which most of the cells are destined to leave within hours or days. Methods for cell separation and nuclear fractionation now permit biochemical studies of those cells that retain or regain the capacity for DNA synthesis and that are likely to include the transformed cell population. Among the changes associated with malignant transformation to be described are alterations in nuclear protein composition and metabolism, qualitative and quantitative differences in adenosine deaminase activities, activation of the guanylate/cyclic GMP system, and modification of both DNA and chromosomal proteins by alkylating carcinogens. DNA modification to produce O6-methylguanine correlates well with the incidence of tumor induction by methylazoxymethanol. Modifications of chromosomal proteins to produce methylated derivatives of lysine and arginine have been observed after the administration of 1,2-dimethylhydrazine. Such changes are likely to lead to aberrant interactions between DNA and regulatory elements in chromatin, and may not be subject to repair.

Amino Acids↗
PubMed1977

Changes in chromosomal proteins in colon cancer: the complexity and DNA-binding properties of tumor-associated proteins and evidence for their association with the malignant state in human colonic epithelium.

The properties of two classes of nonhistone nuclear proteins (NHNP) whose appearance has been correlated with the process of carcinogenesis in the colonic epithelium of rats given 1,2-dimethylhydrazine (DMH) have been investigated. NHNP isolated from adenocarcinomas of the colon were tested for their binding to homologous DNA. The tumor-specific protein class TNP1 (molecular weight ca. 44,000) shows high affinity for DNA while the second class of tumor-specific proteins (TNP2; molecular weight ca. 62,000) does not bind to DNA. When tumor chromatin is subjected to a limited digestion with DNAse I under conditions that are known to preferentially digest active genes, the TNP1 proteins are selectively released, suggesting that this protein fraction is associated with the actively transcribing portions of the genome. The complexity of both tumor-specific protein classes has also been analyzed by two-dimensional gel electrophoresis. This method reveals a high degree of complexity both in TNP1 and TNP2. Protein classes similar to TNP1 and TNP2 that are also found in human colonic adenocarcinomas are not detectable in polyps from familial polyposis-affected patients at times when no sign of malignancy has yet appeared.

Adenocarcinoma↗
PubMed1977

Selective inhibition with sodium cyanate of protein synthesis in colon cancer cells.

Sodium cyanate, which in its tautomeric acidic form, isocyanic acid, acts as a protein carbamylating reagent, has been previously shown to inhibit selectively both DNA and protein synthesis in a variety of solid tumors. We have now compared its effects on protein synthesis in normal colonic epithelium and in colon tumors induced by the administration of 1,2-dimethylhydrazine to rats. The incorporation of 3H-amino acids into cytoplasmic and nuclear protein fractions was suppressed to a much greater extent in the tumor tissue than in colonic epithelial tissue surrounding the tumors of cyanate-treated rats. Despite its effect on tumor protein synthesis in whole animals, cyanate had little or no effect on cultured cells (HT-29) derived from a human adenocarcinoma of the colon, nor on other malignant cell lines such as HeLa S3 cells, chick fibroblasts transformed by the Rous sarcoma virus, mouse Ehrlich ascites tumor cells, or rat Novikoff hepatoma cells. However, the administration of cyanate i.p. does suppress amino acid incorporation by Novikoff hepatoma cells in the peritoneal cavity of rats. The implication that the mechanism of cyanate inhibition of protein synthesis in tumors may require its in vivo metabolism or utilization to produce a postsynthetic modification of circulatory factors is discussed.

Animals↗
PubMed1977

Selective release of chromosomal proteins during limited DNAase 1 digestion of avian erythrocyte chromatin.

Duck erythrocyte chromatin has been treated with DNAase 1 under conditions that are known to digest selectively the structural genes coding for globin mRNAs. This limited digestion releases specific sets of nonhistone chromosomal proteins that are not preferentially released during limited digestion with micrococcal nuclease, which does not selectively attack the globin sequences. Analysis of nucleosome monomer and multimer peaks separated on sucrose gradients after limited digestion with micrococcal nuclease shows that the proteins which are released by DNAase 1 digestion remain associated with the chromatin subunits and can be removed by extraction in 0.5 M NaCl. These proteins are tentatively identified as members of the high mobility group (HMG) proteins (originally described by Goodwin, Sanders and Johns, 1973) in terms of their extractability, electrophoretic characteristics and amino acid composition.

Amino Acids↗
PubMed1977

Studies on the mechanism of phosphorylation of synthetic polypeptides by a calf thymus cyclic AMP-dependent protein kinase.

Synthetic polypeptides were employed as substrates in kinetic analyses of the reaction mechanism for the catalytic subunit of a cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) from calf thymus. This enzyme preparation was shown to catalyze the transfer of phosphate from ATP to histone H1 from calf thymus, as well as to two synthetic polypeptides, Arg-Lys-Ala-Ser-Gly-Pro (H1-6) and Arg-Arg-Lys-Ala-Ser-Gly-Pro (H1-7), corresponding to the amino acid sequence about serine-38 in calf H1. A related, basic heptapeptide corresponding to a sequence from pig liver pyruvate kinase, Leu-Arg-Arg-Ala-Ser-Leu-Gly (K), was also a substrate. The stoichiometry of peptide phosphorylation was established in each case as the transfer of 1 mol of phosphate from the gamma position of MgATP to the serine hydroxyl of 1 mol of the peptide. Steady-state, initial-velocity, kinetic parameters were determined for each substrate, using various concentrations of ATP. Under the conditions used, all synthetic peptides reacted with greater maximum velocities than whole histone H1. Nevertheless, the K(m) for H1, 54 muM, was lower than the K(m) values of the synthetic substrates. The most efficient substrate was peptide K, which had a V(max) of 50.6 mumol/min per mg of kinase and a K(m) of 63 muM. In the absence of peptide substrate no ATPase activity was detectable at a sensitivity of 0.05% of the rate of peptide phosphorylation, suggesting that ATP is not cleaved to form an unstable phosphoenzyme complex. The data are consistent with a sequential reaction mechanism involving a ternary complex between enzyme, polypeptide substrate, and ATP.

Animals↗
PubMed1977

Microinjection analysis of envelope-glycoprotein messenger activities of avian leukosis viral RNAs.

Virion RNA from the avian leukosis virus Rous-associated virus 2 (RAV-2) and poly(A)-containing RNAs from RAV-2-infected chick embryo fibroblasts were microinjected into fibroblasts transformed by the Bryan high-titer strain of Rous sarcoma virus (RSV), which is deficient in viral envelope glycoprotein. Production of infectious RSV following these injections depended upon the viral envelope-messenger activity of the injected RNA. This system constituted a sensitive and rigorous assay system for viral envelope-messenger RNA. It was found that 21S mRNA from RAV-2-infected cells expressed the highest activity, while 35S mRNA expressed comparatively little. In addition, RAV-2-virion RNA expressed little messenger activity. The rate of formation of infectious RSV following 21S mRNA injections reached a peak near 9 hr, which was followed by a rapid decline. Evidence has been obtained that a small fraction of both 35S virion RNA and 35S mRNA from virus-infected cells was encapsulated into virus particles following their injection into virus-producing cells.

Animals↗
PubMed1977

Evidence for the autophagy of microinjected proteins in HeLA cells.

Rhodamine-conjugated proteins were microinjected into living HeLa cells. Fluorescence microscopy was then employed to study their segregation from the cytoplasm into lysosomes. Results obtained in this way were verified when the corresponding unconjugated proteins were localized by autoradiographic, histological, and antibody-staining methods after their microinjection. Most injected proteins were segregated into cytoplasmic granular structures during their removal from cells. As evidence that these were autophagic vacuoles, they were found to contain no detectable acid phosphatase activity upon formation, after which they moved to the juxtanuclear position of lysosomes and appeared to fuse with them. The segregation of microinjected proteins exhibited a high degree of selectivity. The half-times of placement of individual exogenous proteins into cytoplasmic granules varied from 3 h to nearly 3 days, and one protein, hemoglobin, was never observed to enter them. Furthermore, endogenous HeLa proteins in a size fraction near 200,000 daltons were segregated much more rapidly than those in a fraction near 40,000 daltons. In these studies, rapid protein segregation appeared to take place by a mechanism of exclusion of the injected protein from numerous cytoplasmic domains.

Acid Phosphatase↗
PubMed1976

Microinjection studies of duck globin messenger RNA translation in human and avian cells.

Microinjection techniques were used for the study of the translation of heterospecific messenger RNAs in living cells. Duck globin messenger RNAs, in the form of polysomes, messenger ribonucleoprotein particles, or free mRNAs, were injected into cells of human origin (HeLa), and the subsequent appearance and accumulation of avian globin were measured by specific immunofluorescence techniques. Globin accumulated within a high proportion of HeLa cells for at least 25 hr following injection, indicating the intracellular stability of the heterospecific globin messenger RNA and the fact that mRNA initially associated with more complex structures could be translated in the HeLa cytoplasm. In similar experiments, duck reticulocyte polysomes were shown to be translated in duck embryo cells but not in embryonic chick liver cells. The latter, however, could be shown to withstand the microinjection procedure as judged by their capacity to respond normally to inducers and inhibitors of the synthesis of alpha-aminolevulinic acid synthetase. HeLa cells injected with duck hemoglobin divide at normal or nearly normal rates following the injection, but their globin content diminishes, in contrast with the increasing globin content of cells receiving duck reticulocyte polysomes, mRNP particles, or free mRNA.

5-Aminolevulinate Synthetase↗
PubMed1976

The subunit structure of chromatin from Physarum polycephalum.

Nucleosome DNA repeat lengths in Physarum chromatin, determined by nuclease digestion experiments, are shorter than those observed in most mammalian chromatin and longer than those reported for chromatin of certain other lower eukaryotes. After digestion with staphylococcal nuclease for short periods of time an average repeat length of 190 base pairs is measured. After more extensive digestion an average repeat length of 172 base pairs is measured. Upon prolonged digestion DNA is degraded to an average monomer subunit length of 160 base pairs, with only a small amount of DNA found in lengths of 130 base pairs or smaller. Mathematical analysis of the data suggests that the Physarum nucleosome DNA repeat comprises a protected DNA segment of about 159 base pairs with a nuclease-accessible interconnecting segment which ranges from 13 to 31 base pairs. The spacing data are compatible with measurements from electron micrographs of Physarum chromatin.

Animals↗
PubMed1976

Characteristic complements of nuclear nonhistone proteins in colonic epithelial tumors.

Nuclei were isolated from colonic epithelial tumors induced in rats by the administration of 1,2-dimethylhydrazine. The nuclei were fractionated according to buoyant density by centrifugation in discontinuous sucrose density gradients. Nuclei differing in density differ in size, nonhistone protein-to-DNA ratio, and DNA synthetic activity. Their distribution in a density gradient also reflects their histological localization in the layers of the intestinal mucosa, as judged by the nuclear capacity for [3H]thymidine incorporation into DNA in vivo. Different nuclear classes isolated from the tumors contain characteristic complements of nuclear nonhistone proteins. Particularly striking accumulations of two protein classes with molecular weights of ca. 44,000 and 62,000 occur during carcinogenesis. These proteins are not uniformly distributed throughout all nuclear classes derived from the tumors. They are not at all prominent in normal colonic epithelial nuclei or in epithelial cells surroundign the tumors, or in the liver nuclei of animals treated with 1,2-dimethylhydrazine. Procedures for the differential extraction of these protein classes are described. Similar nuclear proteins have been detected in human colonic tumors and in a human cell line (HT-29) derived from an adenocarcinoma of the colon. The selective accumulation of such proteins in colonic tumor nuclei may have diagnostic value.

Adenocarcinoma↗
PubMed1975

DNA binding by cyclic adenosine 3',5'-monophosphate dependent protein kinase from calf thymus nuclei.

Cyclic adenosine 3',5'-monophosphate (cAMP) dependent protein kinase and proteins specifically binding cAMP have been extracted from calf thymus nuclei and analyzed for their abilities to bind to DNA. Approximately 70% of the cAMP-binding activity in the nucleus can be ascribed to a nuclear acidic protein with physical and biochemical characteristics of the regulatory (R) subunit of cAMP-dependent protein kinase. Several peaks of protein kinase activity and of cAMP-binding activity are resolved by affinity chromatography of nuclear acidic proteins on calf thymus DNA covalently linked to aminoethyl Sephrarose 4B. When an extensively purified protein kinase is subjected to chromatography on the DNA column in the presence of 10(-7) M cAMP, the R subunit of the kinase is eluted from the column at 0.05 M NaCl while the catalytic (C) subunit of the enzyme is eluted at 0.1-0.2 M NaCl. When chromatographed in the presence of histones, the R subunit is retained on the column and is eluted at 0.6-0.9 M NaCl. In the presence of cAMP, association of the C subunit with DNA is enhanced, as determined by sucrose density gradient centrifugation of DNA-protein kinase complexes. cAMP increases the capacity of the calf thymus cAMP-dependent protein kinase preparation to bind labeled calf thymus DNA, as determined by a technique employing filter retention of DNA-protein complexes. This protein kinase preparation binds calf thymus DNA in preference to salmon DNA, Escherichia coli DNA, or yeast RNA. Binding of protein kinases to DNA may be part of a mechanism for localizing cyclic nucleotide stimulated protein phosphorylation at specific sites in the chromatin.

Animals↗