ISSN:0021-9541    

DOI:10.1002/jcp.1041010302

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

年代:1979

数据来源: WILEY

摘要:

AbstractA mutant of BHK cells (ts422E) temperature‐sensitive for processing 32S rRNA to 28S rRNA (Toniolo et al., '73) also loses the ability to synthesize polyamines and 5.8S rRNA when shifted to the non‐permissive temperature (39°). The activity of several enzymes not involved with polyamine synthesis, methylation of 32S rRNA, and small nuclear RNA production are apparently unaffected after at least 24 hours at 39°. When cultures are returned to the permissive temperature (33°), polyamine synthesizing capacity returns to normal as mature rRNA production r

ISSN:0021-9541    

DOI:10.1002/jcp.1041010303

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

年代:1979

数据来源: WILEY

摘要:

AbstractCyclic AMP (cAMP) causes growth arrest in G1and induction of cAMP phosphodiesterase and decrease of ornithine decarboxylase in S49 mouse lymphoma cells. Dibutyryl cAMP treatment of partially synchronized cells causes similar changes in activities of both enzymes, regardless of position in the cell cycle. This suggests that cAMP regulation of these enzymes is not mediated by growth perturbation.

ISSN:0021-9541    

DOI:10.1002/jcp.1041010304

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

年代:1979

数据来源: WILEY

摘要:

AbstractSubcellular organelles from livers of rats three days prenatal to 50 weeks postnatal were separated on sucrose gradients. The peroxisomes had a constant density of 1.243 g/ml throughout the life of the animal. The density of the mitochondria changed from about 1.236 g/ml at birth to a constant value of 1.200 g/ml after two weeks.The peroxisomal and mitochondrial fatty acid β‐oxidation and the peroxisomal and supernatant activities of catalase and glycerol‐3‐phosphate dehydrogenase were measured at each age, as well as the peroxisomal core enzyme, urate oxidase, and the mitochondrial matrix enzyme, glutamate dehydrogenase. All of these activities were very low or undetectable before birth. Mitochondrial glutamate dehydrogenase and peroxisomal urate oxidase reached maximal activities per g of liver at two and five weeks of age, respectively.Fatty acid β‐oxidation in both peroxisomes and mitochondria and peroxisomal glycerol‐3‐phosphate dehydrogenase exhibited maximum activities per g of liver between one and two weeks of age before weaning and then decreased to steady state levels in the adult. Peroxisomal β‐oxidation accounted for at least 10% of the total β‐oxidation activity in the young rat liver, but became 30% of the total in the liver of the adult female and 20% in the adult male due to a decrease in mitochondrial β‐oxidation after two weeks of age. The greatest change in β‐oxidation was in the mitochondrial fraction rather than in the peroxisomes. At two weeks of age, four times as much β‐oxidation activity was in the mitochondria as in the peroxisomal fraction. Peroxisomal glycerol‐3‐phosphate dehydrogenase activity accounted for 5% to 7% of the total activity in animals younger than one week, but only 1% to 2% in animals older than one week.Up to three weeks of age, 85% to 90% of the liver catalase was recovered in the peroxisomes. The activity of peroxisomal catalase per g of rat liver remained constant after three weeks of age, but the total activity of catalase further increased 2.5‐ to 3‐fold, and all of the increased acti

ISSN:0021-9541    

DOI:10.1002/jcp.1041010305

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

年代:1979

数据来源: WILEY

摘要:

AbstractTemporal inhibition of protein synthesis with cycloheximide prevents subsequent insulin, but not serum‐stimulated DNA synthesis in G1‐arrested chick embryo fibroblasts (CEF). The inhibition is measured by the incorporation of3H‐thymidine into acid insoluble material and confirmed by chemical estimate of the DNA content of inhibited and uninhibited cells. Cycloheximide treatment is without effect if the cell cultures are maintained at 4° C while exposed to the drug. Several α‐keto acids (pyruvate, oxaloacetate, α‐keto‐butyrate) at 0.5‐1 mM concentrations restore DNA synthesis in previously inhibited cells when combined with insulin. L‐alanine (D‐alanine is inert) is even more effective than the keto acids in stimulating DNA synthesis after cycloheximide treatment. Clucose transport was unaffected by cycloheximide treatment while lactate levels in medium from inhibited, insulin‐stimulated CEF were reduced 70% compared to uninhibited counterparts. We speculate that cycloheximide treatment may lead to the decay of a glycolytic enzyme which compromises the ability of inhibited cells to synthesize pyruvate from glucose, and thus induces an exogenous requirement for α‐keto acid or L‐alanine. A serum component(s) with a molecular weight of about 100 permitted insulin‐stimulated DNA

ISSN:0021-9541    

DOI:10.1002/jcp.1041010306

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

年代:1979

数据来源: WILEY

摘要:

AbstractCultures of heat‐synchronizedTetrahymena pyriformis, growing in a proteose peptone medium, were subjected to short pulses of the amino acid analogue,p‐flurophenylalanine, and high hydrostatic pressure. The pulses of these agents were chosen so that, when applied individually, they did not appreciably delay cell division. However, combined treatments, analogue pulse followed by pressure pulse, produced a pronounced synergism. The results are interpreted as further evidence to support the inclusion of analogue division proteins in pressure labile assemblies during the progression ofTetrahymenainto divis

ISSN:0021-9541    

DOI:10.1002/jcp.1041010307

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

年代:1979

数据来源: WILEY

摘要:

AbstractWhen replicating DNA is labeled sequentially with radioactive and density tracers and analyzed by equilibrium centrifugation, the fraction banding at heavier than normal density is inversely proportional to the rate of replication fork movement if there is a sharp transition from one tracer to the other on the newly synthesized chains (Painter and Schaefer, '69). Primate CV‐1 DNA labeled for 5 to 30 minutes with3H‐dThd and then for three hours with BrdUrd in the presence of FdUrd bands in a bimodal distribution in alkaline CsCl, rather than in a continuous distribution with a skew toward heavier density seen when FdUrd is omitted and centrifugation is in neutral CsCl. The heavy density peak represents interspersion of both tracers in the DNA and is caused by slow transition from dThd to BrdUrd incorporation when the tracers are switched in the labeling medium. This may result from preferential uptake and incorporation of dThd over BrdUrd. Because of the interspersion, calculation of the rate of replication fork movement is inaccurate. Reversal of the labeling sequence with administration of the long density pulse before the radioactive pulse reduces the problem of interspersion. Using this sequence of labeling, estimates of the rate of fork movement of 0.36–0.38 μm/min are obtained when the3H pulse time is long enough to allow accurate measurement of the fraction of heavy DNA. Analysis by fiber autoradiography yields a rate of 0.56 μm/min in the same cell line. If appropriate precautions are taken to minimize mixing of the two tracers in the precursor pool and to ensure that the fraction of heavy DNA is measured accurately, the hydrodynamic technique provides an objective method of measuring rate of fork movement that gives values only slightly lower than those obtained by autoradi

ISSN:0021-9541    

DOI:10.1002/jcp.1041010308

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

年代:1979

数据来源: WILEY

摘要:

AbstractA variant endothelial cell type was found to arise spontaneously from cultures of bovine aortal endothelial cells. This variant showed no contact inhibition and overgrew confluent cultures of wild‐type endothelial cells. Unlike other reported variants of this cell type produced by chemical mutagenesis or by withdrawal of polypeptide growth factor, this variant retained the capacity to synthesise factor VIII antigen, but showed no alteration from wild‐type in capacity to adsorb platelets. The variant also had an increased capacity to bind FITC‐conjugated con A to its su

ISSN:0021-9541    

DOI:10.1002/jcp.1041010309

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

年代:1979

数据来源: WILEY

摘要:

AbstractExtracts of submaxillary glands from two different strains of inbred mice were mitogenic for human endothelial cells in culture. The mitogenic activity of extracts from glands of males of the SWR/J and C57BL/10J strains were equivalent, and the growth stimulating effect was unrelated to renin or esteroproteolytic activity. Mitogenic activity in extracts from SWR/J females was less than that from males, and extracts from C57BL/10J females were inactive. The polypeptide growth factors, epidermal (EGF) and fibroblast (FGF) growth factors, also stimulated replication of endothelial cells. Cells from either umbilical arteries or veins responded to submaxillary extracts, EGF, or FGF with a similar increase in cell number, increase in protein and enhanced uptake of3H‐thymidine. The proliferative response was associated with decreased activity of angiotensin I converting enzyme which is localized on the endothelial surface. Nerve growth factor (NGF) was not mitogenic for endothelial cells. Extracts of submaxillary glands from male mice of either strain contained approximately 20 times more EGF than extracts from females, as determined by immunodiffusion. Mitogenic activity of the extracts was completely inhibited by antiserum to EGF, suggesting that the active component of these preparations is EG

ISSN:0021-9541    

DOI:10.1002/jcp.1041010310

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

年代:1979

数据来源: WILEY

摘要:

AbstractLeupeptin, chymostatin and antipain inhibited the degradation of long‐lived proteins in cultured rat hepatocytes by 20–30%, probably by inhibiting lysosomal proteases:(1) Leupeptin and chymostatin decreased to a similar extent the degradation of an exogenous protein125I‐asialo fetuin, a process known to occur within lysosomes. (2) In extracts of cells treated with leupeptin, cathepsin B activity was inhibited by 35–50%. (3) Leupeptin, chymostatin and antipain inhibited proteolysis by homogenates of liver lysosomes but not by the supernatant fraction. These agents, however, do not appear to rapidly permeate the membrane of isolated lysosomes.Leupeptin, chymostatin and antipain did not inhibit the breakdown of short‐lived normal cell proteins, and ones containing amino acid analogs. Even when the amount of abnormal proteins was increased, such that it comprised a large fraction of cell protein, the degradation of these polypeptides was still very rapid and not affected by these inhibitors. The pathway for the degradation of short‐lived cell proteins thus appears distinct from that responsible for degradation of long‐lived cell proteins. In accord with this conclusion, reduction of the temperature of cultures inhibited the breakdown of long‐lived proteins to a much greater extent than it affected the breakdown of short‐lived ones.Treatment of cultured hepatocytes with glucagon, or deprivation for serum or amino acids stimulated the degradation of the more stable cell proteins but did not affect the breakdown of125I‐asialo‐fetuin. Under these conditions leupeptin and chymostatin inhibited the breakdown of long‐lived cell proteins to the same extent as in control cultures. Thus, lysosomal enzymes seem to play an important role in protein breakdown both in fed hepatocytes and in cells where pro

ISSN:0021-9541    

DOI:10.1002/jcp.1041010311

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

年代:1979

数据来源: WILEY