摘要:

AbstractThe incorporation of3H‐labeled deoxyadenosine and deoxyguanosine into nucleic acids by cultured Novikoff rat hepatoma cells is about 80% into RNA and 20% into DNA. The pathways of incorporation have been elucidated in studies with whole cells and cell‐free extracts. Deoxyadenosine is very rapidly deaminated to deoxyinosine. Most of the deoxyinosine formed by whole cells is transported out of the cells and accumulates in the medium. A portion of the deoxyinosine, and deoxyguanosine are phosphorolyzed by purine nucleoside phosphorylase to hypoxanthine and guanine, respectively. The latter are subsequently converted by hypoxanthine‐guanine phosphoribosyl transferase to IMP and GMP, respectively. Incorporation of the purine deoxyribonucleosides into DNA is mainly via this pathway and the subsequent reduction of ADP and GDP by ribonucleoside reductase, although a small proportion of the deoxyadenosine and deoxyguanosine taken up by the cells seems to be directly phosphorylated to dAMP and dGMP, respectively. Deoxyguanosine is incorporated only into guanine residues of RNA and DNA. Deoxyadenosine is also mainly incorporated into guanine residues of RNA and DNA, although the radioactivity of deoxyadenosine in the acid‐soluble pool is almost exclusively associated with ATP. A similar labeling pattern is observed with labeled deoxyinosine, inosine or hypoxanthine. The pyrimidine deoxyribonucleosides, on the other hand, are specific precursors for their respective bases in DNA.Hydroxyurea inhibits the incorporation of all deoxyribonucleosides into DNA. Results from pulse‐chase experiments indicate that the inhibition of DNA synthesis is prevented by the presence of high concentrations of deoxyadenosine plus deoxyguanosine in the medium. Either purine deoxyribonucleoside alone or deoxycytidine, hypoxanthine or inosine alone or in combination with deoxyadenosine or deoxyguanosine are ineffective. The results are consistent with the conclusion that the inhibition of DNA synthesis is due to a depletion of the dATP and dGTP pools as a result of the hydroxyurea treatment. On the other hand, hydroxyurea causes an increased incorporation of thymidine and deoxycytidine into the dTTP and dCTP pools, respectively. Evidence is presented to indicate that this effect of hydroxyurea is due to an increased synthesis of dTTP and dCTP rather than to an inhibition of their

ISSN:0021-9541    

DOI:10.1002/jcp.1040830302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe transport of various deoxyribonucleosides by cultured Novikoff rat hepatoma cells (subline N1S1‐67) follows normal Michaelis‐Menten kinetics. The transport reactions are competitively inhibited by most heterologous deoxy‐ and ribonucleosides and by Persantin and Cytochalasin B. Comparisons of the transport kinetics of the various deoxyribonucleosides (Kmand Vmax) and of the Km/Kiratios for the inhibitions indicate that deoxythymidine, deoxyuridine and 5‐fluordeoxyuridine are transported by a single system, whereas deoxycytidine and the purine deoxyribonucleosides are transported by other systems. The data suggest that deoxyadenosine, deoxyguanosine and deoxyinosine, are not transported by a single system, but the number of transport systems involved could not be established unequivocally. Similar comparisons also suggest that the deoxyribonucleosides are transported by different systems than the ribonucleosides. All deoxyribonucleoside transport systems are inhibited to about the same extent by Persantin (Ki= 1–2 μM) and Cytochalasin B (Ki= 4–12 μM). The inhibitions of deoxynucleoside transport resulted in corresponding apparent competitive inhibitions of their incorporation into

ISSN:0021-9541    

DOI:10.1002/jcp.1040830303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractOrnithine decarboxylase activity in high density, stationary phase rat hepatoma (HTC) cells in suspension culture has an extremely short half‐life of between 5 and 15 minutes, as measured after inhibiting protein synthesis. Following dilution of these cells into fresh medium there is a large increase in ornithine decarboxylase activity, reaching a peak often several hundred times the initial level at about four hours. At least part of this stimulation is due to an increase in the apparent half‐life of the enzyme, to between 30 and 90 minutes. Evidence is presented that the supply of amino acids can control the turnover of ODC under some conditions. For example supplementing high density cells with glutamine, asparagine, serine, glycine and proline, either singly or together, increases ODC activity and decreases its apparent turnover. The stimulation by amino acids is enhanced by se

ISSN:0021-9541    

DOI:10.1002/jcp.1040830304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractHTC cells incubated in the absence of serum for more than 14 hours have very low levels of ornithine decarboxylase, the first enzyme on the pathway of polyamine synthesis. Readdition of serum causes an increase in the activity of ODC, reaching a maximum on average 17 times above the basal level after five hours. This increase is due in part to a decrease in the apparent rate of degradation of ODC, and also to a stimulation of its synthesis. Within the first two hours the serum induction of ODC is resistant to Actinomycin D. Insulin at 5 μm/ml alsocauses an increase in ODC activity but only after a delay of two hours, in contrast to its more rapid stimulation of tyrosine transaminase activity

ISSN:0021-9541    

DOI:10.1002/jcp.1040830305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe effect of increasing calcium concentrations on the electrophoretic mobility of cells obtained from early chick blastoderms at successive developmental stages was studied. Cells had zero mobilities at calcium concentrations in the range of 1 to 2 × 10−2M CaCl2, and became positively charged when calcium concentrations between 2 and 5 × 10−2M CaCl2were used. Results using trypsin suggest that while some calcium binding sites disappear from the surface ionogenic layer, the majority of them are not removed by this enzyme. The calcium binding capacity did not vary appreciably in the stages studied. Charge reversal induced by calcium is rever

ISSN:0021-9541    

DOI:10.1002/jcp.1040830306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractMouse peritoneal exudate cells induced by thioglycollate medium can form colonies in soft agar with a plating efficiency of about 5% (0.6%–10%). Cells from an unstimulated peritoneal cavity form no colonies or have a plating efficiency of less than 0.001 %. These colony‐forming cells from the peritoneal exudate are similar to bone marrow colony‐forming cells in vitro in that they both require a substance(s) present in conditioned medium from L‐cells or mouse embryo fibroblasts or the serum from endotoxin‐treated mice for the initiation and the continuation of their growth. However, peritoneal exudate colony‐forming cells have a much longer initial lag period (10–14 days) and can survive longer in the absence of L‐cell conditioned medium than bone marrow colony‐forming cells. Only mononuclear cells, presumably macrophages, are observed in peritoneal exudate colonies, whereas bone marrow cell colonies contain both polymorphonuclear cell

ISSN:0021-9541    

DOI:10.1002/jcp.1040830307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe behavior of two established cell lines was found to vary when subcultivated on protein polymers covered with either negatively or positively charged substances. Results indicate that the influence on cell behavior is conditioned by the charge rather than by structural differences or degree of attachment of the substances to the polymer. Furthermore, the substratum seems to have just a physical effect at the cell membrane without any direct influence on cell metabolism.Cells were also seeded on a calf serum polymer and it was found that serum loses its properties on cultivated cells when used as substratum.

ISSN:0021-9541    

DOI:10.1002/jcp.1040830308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractMore than 80% of the intracellular pyridine metabolite pool of human culture cells is trapped by OsO4fixation. The fixed pyridine metabolites fully exchange with nicotinamide and nicotinic acid but not with nicotinamide adenine dinucleotide. Yet, chromatography of the exchanged compounds reveals that NAD and NADP constitute more than 95%. of the fixed material. Although the mechanism of OsO4fixation is not fully understood, such fixation has permitted the autoradiographic detection of intracellular pyridine metabolites. Cells of the human cell line, D98/AH2, synthesize pyridine nucleotides during all phases of the cell cycle at rates which do not vary by more than six‐fold. There is no difference in the apparent concentration of pyridine metabolites between nucleus and cytoplasm after ten minute or three day pulses with3H‐nicotinic acid. The3H‐labeled pyridine ring is lost from D98/AH2 cells upon transfer to unlabeled medium. In general, the rate of loss is uniform among cells in the population. However, in a small proportion of cells there is little or no loss. Non‐dividing cells lose the pyridine ring at approximately the same rate as dividing cells, yet the intracellular concentration of pyridine metabolites is 50% greater in non‐divid

ISSN:0021-9541    

DOI:10.1002/jcp.1040830309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractNine variant cell lines isolated from cloned 7,12‐dimethylbenz(a) ‐ahthracene transformed Balb/3T3 mouse cells by treatment with FUdR had growth parameters closely resembling nontransformed cells. Chromosome analysis of the variant lines demonstrated that six variants had a diminished number and three variants had an increased number of chromosomes compared to the parental transformed cell line. All variants had unique marker chromosomes not present in the parental transformed Balb/3T3 cells. The distribution of marker chromosomes and heterochromatin suggested that the initial event in variant formation was a reduction in chromosome number with a subsequent polyploidization of the reduced chromosome complem

ISSN:0021-9541    

DOI:10.1002/jcp.1040830310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThymocytes incubated as cell suspensions in vitro are known to be markedly dependent upon added glucose for maintenance of maximal rates of incorporation of radiolabelled amino acids into protein. This requirement is only partially satisfied by other added substrates, such as pyruvate. Evidence is presented that incorporation of amino acids into protein associated with the nuclear fraction isolated from these cells is more dependent upon added glucose than is labelling of protein found in the rest of the cell.The dependence of the labelling of nuclear protein upon glucose is shown by comparing the ability of glucose and pyruvate to stimulate the incorporation of [14C‐L] valine into the protein of nuclear and cytoplasmic fractions of thymus cells. The fractions are isolated on sucrose gradients after incubating suspensions of cells in substrate‐free medium for two hours, adding carbohydrates and labelled L‐valine for 30 min and then stopping the incubation by breaking the cells with hypotonic shock. When the protein‐synthetic stimulatory effects of glucose and pyruvate are compared, glucose is almost equally capable (90%) at stimulating rates of protein synthesis in nuclear compared to cytoplasmic fractions. Pyruvate is much less effective in nuclear than in cytoplasmic fractions (30%).Evidence is also presented from pulse‐chase experiments that the glucosedependent labelling of protein associated with the nuclear fraction occurs within that fraction, as opposed to migration to the nuclear fraction after being synthesized elsewhere.It is suggested from these and other data that a unique ability of glucose to provide non‐mitochondrial ATP to the nucleus may be central to the dependence of the labelling of nuclear protein on thi

ISSN:0021-9541    

DOI:10.1002/jcp.1040830311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY