摘要:

AbstractDilution of a stationary phase culture of Scarlet Rose results in an increased rate of protein synthesis. This study compares the time course of this increase with the changes in polyribosome content and the levels of adenine and guanine nucleotides.During the first two hours after dilution, protein synthesis increases 2‐ to 3‐fold; much of the large monoribosome pool that characterizes the stationary state disappears and a steady state situation is reached in which 70% of the ribosomes are in polyribosomes. Between two and eight hours, there is no further change in polyribosome content although the rate of protein synthesis increases an additional 2‐ to 3‐fold. During this initial 8‐hour period there is little change in the levels of ATP and GTP. An explanation consistent with these observations is that the initial activation (within the first 2 hours), characterized by the monoribosome to polysome transition, is at the level of a component(s) of the initiation system, and that between two and eight hours, since neither mRNA availability nor energy level are primary determinants, protein synthesis is augmented by the activation of a translational component, perhaps an elongation factor.After 24 hours, there is a proliferative phase characterized by the onset of ribosome accumulation. By day 5, maximum ribosome levels, 5‐fold that of 24‐hour cells, are reached, but the rate of protein synthesis increases only 2.5‐fold during this period. The lack of quantitative coincidence between the changes in polyribosome content and the rates of protein synthesis again suggests that factors other than mRNA availability are involved in determining the overall rate of protein synthesis. Finally at days 6–8, while the growth of the culture is still in the exponential phase, the rate of protein synthesis per unit fresh weight drops markedly concomitant with a decline in ribosome content. At days 11–12, the monoribosome to polysome ratio begins to change with the monoribosome pool increasing.Presence of either actinomycin D or cordycepin inhibits increased protein synthesis in direct relation to the ability of these compounds to inhibit RNA synthesis. This suggests that the protein synthetic processes occurring after dilution require either the synthesis of the mRNA that is being translated or of an RNA functioning in a clos

ISSN:0021-9541    

DOI:10.1002/jcp.1040930302

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

年代:1977

数据来源: WILEY

摘要:

AbstractAt 43°C (but not at 41°C), organic solvents used to dissolve water‐insoluble chemotherapeutic agents become themselves lethal to cells. This finding is not unique to Chinese hamster cells (HA‐1); mouse mammary sarcoma cells (EMT‐6) behave similarly. The solvent concentrations involved are in the range of those needed to make drug solutions. Hence experiments measuring drug‐cell interactions at elevated temperatures must include controls which independently measure solven

ISSN:0021-9541    

DOI:10.1002/jcp.1040930303

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

年代:1977

数据来源: WILEY

摘要:

AbstractVarious biochemical properties of mitochondria isolated from primary monolayer cultures of mammary epithelial cells from mid‐pregnant or hormonally stimulated mice were examined daily for seven or eight days. When compared with mitochondria from mammary glands of mid‐pregnant animals, the specific activities of several mitochondrial enzymes were greatly reduced in cells after seven days in culture. There was a 5‐ to 6‐fold reduction in the specific activities of cytochrome oxidase, succinate dehydrogenase and α glycerophosphate oxidase while malate dehydrogenase and adenylate kinase activities were 2‐ to 3‐fold lower. The reduction in mitochondrial enzyme activities was gradual and related to the length of time the cells were in culture. Progressive changes were also seen in the electrophoresis profiles of mitochondrial proteins in SDS‐urea polyacrylamide gels. Mitochondria isolated from 1‐, 2‐, 3‐ and 8‐day cell cultures showed a continuous reduction in the relative amounts of several mitochondrial polypeptides in the gel profiles. Addition of35S‐methionine to cell cultures for short and long periods indicated that mitochondrial protein synthesis continued throughout the 8‐day culture period. However, the synthesis of several particular polypeptides was reduced progressively during the culture period. These studies indicate that mouse mammary epithelial cells have a lowered capacity for respiratory metabolism as a result of specific mitochondrial alterations which might be associated with the general loss of differentiated morphology by those cell

ISSN:0021-9541    

DOI:10.1002/jcp.1040930304

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

年代:1977

数据来源: WILEY

摘要:

AbstractHS3, a highly phosphorylated dinucleoside originally purified from the fungusAchlya, has been isolated from Chinese hamster ovary cells undergoing glutamine starvation. The HS3 compounds obtained from the fungal and mammalian sources exhibited similar physical and chemical properties. This unusual dinucleotide may be an important regulator of eucaryotic ribonucleoside diphosphate reductase activity; for 50 μm HS3, isolated from either mammalian or fungal cells, significantly inhibited CDP reduction inAchlyaor hamster cell preparations, but only marginally affected the activity of the enzyme fromE.coli. Studies with HS3 isolated fromAchlyaand partially purified mammalian ribonucleotide reductase indicated that the compound noncompetitively inhibited the reduction of varying concentrations of the substrates CDP, ADP and GDP with Ki values of 23 μm, 14 μM and 16 μM respectively. These inhibitor concentrations are well below the estimated intracellular levels of HS3 in glutamine starved cells and suggest that HS3 inhibition of ribonucleotide reduction may be responsible for the rapid inhibition of DNA synthesis seen under these culture conditi

ISSN:0021-9541    

DOI:10.1002/jcp.1040930305

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

年代:1977

数据来源: WILEY

摘要:

AbstractShortly after the withdrawal of L‐glutamine from the growth medium of Chinese hamster ovary (CHO) cells, the rate of synthesis of a bizarre dinucleoside polyphosphate, HS3, increased by 5‐ to 6‐fold. This elevated rate of synthesis was maintained for six hours before it gradually declined to basal level 22 hours later. The pool size of HS3 increased and decreased coincidentally with rate changes. Withdrawal of L‐isoleucine did not affect HS3 biosynthesis. A glycine, adenosine, thymidine (GAT−) auxotroph of CHO cells accumulated HS3 when adenosine, not glutamine, was withdrawn. Replenishment of either glutamine (“wild type” cells) or adenosine (GAT−cells) caused an immediate depletion of HS3 intracellularly.When HS3 accumulated in CHO cells, DNA and RNA synthesis decreased and,vice versa. A similar correlation was not seen for protein synthesis. But, inhibition of protein synthesis by either puromycin or cycloheximide, and of RNA biosynthesis by actinomycin D facilitated HS3 depletion in L‐glutamine starved cells.Mutant CHO cells that are deficient in purine salvage metabolism, HGPRT−(hypoxanthine‐guanine phosphoribosyltransferase) failed to deplete their accumulated HS3 when fed with hypoxanthine, whereas the “wild type” CHO cells responded accordingly. The available data suggest that HS3 metabolism is connected withde novoand salvage pathways of nucleotide biosynthesis, and may play a crucial role in regulating nucleic acid metabolism in CHO cells under conditi

ISSN:0021-9541    

DOI:10.1002/jcp.1040930306

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

年代:1977

数据来源: WILEY

摘要:

AbstractWe have found cyclic AMP in the large, heterotrichous ciliateStentor coeruleusin amounts per milligram protein similar to those found in another ciliate,Tetrahymena pyriformis. The possible function of cyclic AMP inStentorwas first examined by determining its effects on oral regeneration, the process by whichStentorcan replace a missing oral apparatus in eight to ten hours. Once begun (by brief exposure to a 15% sucrose solution, causing shedding of the oral apparatus) regeneration follows eight specific morphological stages visible with the dissecting microscope. Continuous exposure of regenerating cells to either N6, 2′‐0‐dibutyryl adenosine cyclic 3′:5′‐monophosphate (DBC) or theophylline begun at the onset of oral regeneration (stage 0) caused delays in the completion of regeneration. The delays induced by DBC occurred in the early stages prior to stage 5. Regenerating cells exposed to DBC or theophylline at various stages of development were delayed, even at stages 5 and 6. Both DBC and theophylline reversibly bleached the cortical pigment of the cells. Guanosine 3′:5′‐cyclic monophosphate (cyclic GMP), AMP, GMP, and sodium butyrate neither delayed oral regeneration nor bleached the cortical pigment. Excess extracellular calcium ions alone had no effect on oral regeneration, but 10 mM calcium and DBC caused more delay than DBC alone. Thus, the delay of oral regeneration inStentorcaused by cyclic AMP may involve calcium ions.To determine if cyclic AMP can retard in situ ciliary regeneration byStentor, as it does inTetrahymena, a new technique, more accurate than past methods, was developed to monitor ciliary regrowth. Using this procedure we found that both DBC and theophylline significantly delayed the in situ ciliary regen

ISSN:0021-9541    

DOI:10.1002/jcp.1040930307

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe rapid catabolism of glutamine by the cultured human lymphoblast line WI‐L2 can be inhibited greater than 95% by incubation of cell suspensions with 6‐diazo‐5‐oxo‐L‐norleucine (DON). The inhibition persists for at least four hours after removal of DON from the cell suspension. The exposure of cells to DON inhibits over 95% of the glutaminase activity measured in lysates in the presence of either phosphate or maleate. Similarly, γ‐glutamyl transpeptidase, assayed with γ‐glutamyl‐p‐nitroanilide as substrate and glycylglycine as acceptor, is inhibited over 90%. DON‐treated and control cells accumulated radioactive material from suspensions containing [14C]‐L‐glutamine at similar initial rates; the radioactive material accumulated by the DON‐treated cells is all recoverable as glutamine while the radioactive material accumulated by untreated cells is princ

ISSN:0021-9541    

DOI:10.1002/jcp.1040930308

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

年代:1977

数据来源: WILEY

摘要:

AbstractIn the presence of tetraethylammonium or barium ions, the larval muscle fibers ofDrosophila melanogasterwere found to produce an all‐or‐none action potential operated by the calcium channels. The development of this distinctive membrane property during the maturation of muscle cells was studied by measuring the maximum rate of rise of the action potential in the larval muscle fibers at different stages of development from the sixteenth to ninety‐sixth hours after hatching. The value increased significantly with age until a peak was reached at the sixty‐fourth hour, although it became lower again as puparium formation neared at about the ninety‐sixth hour. This suggests that during larval development the muscle fibers develop the ability to generate an action potential due to an inward current through the calcium channels, although the ability became lower at the later stage of larval de

ISSN:0021-9541    

DOI:10.1002/jcp.1040930309

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

年代:1977

数据来源: WILEY

摘要:

AbstractCultured fibroblasts derived from human keloid tissue are presented as a possible model system for studying the genetic regulation of cell growth. Histamine is shown to have a marked effect on the growth of cultured fibroblasts. A small increase in growth rate is seen during the log phase of the culture cycle and a 50% increase in cell number is observed during the plateau phase. Differences in the extent of growth stimulation are observed between strains isolated from different individuals. While most strains showed approximately 50% stimulation, a few were not stimulated and some strains gave a 100% or greater increase in cell number due to histamine. This phenotypic difference in extent of growth stimulation in response to histamine cannot be attributed to the gene or genes for keloid formation. However, elevated levels of histamine in vivo may be a contributing factor to the abnormal cell growth observed in this disorder. The extent of growth stimulation due to histamine decreases with repeated subculturing.

ISSN:0021-9541    

DOI:10.1002/jcp.1040930310

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

年代:1977

数据来源: WILEY

摘要:

AbstractDBcAMP reversibly arrests cultivated Cloudman melanoma cells in the late S and G2 phases of the cell cycle. This is supported by the measurement of DNA synthesis by autoradiography and measurement of cellular DNA by two methods—the diphenylamine reaction and microspectrophotometry of Feulgen stained cells. We also present evidence that (1) cell division is prevented if DBcAMP is added as late in the cycle as early S phase. (2) The inhibition of cell division does not appear to be caused by products of tyrosine oxidation. (3) The increase in cell size that occurs in the presence of DBcAMP reflects continued synthesis of protein in the absence of cell divisio

ISSN:0021-9541    

DOI:10.1002/jcp.1040930311

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

年代:1977

数据来源: WILEY