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Biomedical subjects

L Hayflick

Publications and source records attributed to L Hayflick.

At least 73 records · Page 4Linked to original sources
PubMed1976

Urea-hydrolyzing activity of a T-strain mycoplasma: Ureaplasma urealyticum.

The urea-hydrolyzing activity of a T-strain mycoplasma was studied in experiments using whole cells and cell-free enzyme preparations by measuring the release of 14CO2 from [14C]urea. Under the conditions used, the urea concentration optimum is approximately 5.6 X 10(-3) M urea. The activity is soluble and not membrane bound. It is stable at -70 C for several weeks but is more labile at higher temperatures. The pH optimum is between 5.0 and 6.0. The effect of several inhibitors on the activity was tested and revealed similarities, as well as differences, between T-strain mycoplasma urease activity and the urease activity of other organisms and plants.

Bacteriolysis↗
PubMed1975

Use of biochemical lesions for selection of human cells with hybrid cytoplasms.

Techniques for preparing large populations of anucleate cytoplasms from cultured eukaryotic cells have only recently been described. The principal value of anucleate cytoplasms derives from studies that can be done after they are fused to whole cells. Since present methods for the isolation of heterokaryons are unsuitable for the selection of hybrids between whole cells and anucleate cytoplasms (heteroplasmons), a selective system has been developed which is based on the capacity of anucleate cytoplasms containing active enzymes to rescue whole cells poisoned with iodoacetate. Ethidium bromide, a partially effective agent, was used in conjunction with iodoacetate to demonstrate the feasibility of selecting heterokaryons by producing complementary biochemical lesions in the parental cell strains. The potential for artifact in these systems is not, however, entirely precluded.

Binding Sites↗
PubMed1975

Some effects of growth medium composition on the antigenicity of a T-strain mycoplasma.

T-strain 960 was passaged through 24 serial 10-fold dilutions in media without added urea and with porcine serum albumin fraction V as the only protein enrichment. The organism, either grown in this manner or passaged an additional three times in medium containing horse serum and 0.1 per cent urea, was inoculated into rabbits. Resultant antisera were tested for activity against T-960 growing in these different media by: (i) growth curve analysis in the presence of antiserum, (ii) metabolic inhibition in the presence or absence of complement (fresh guinea pig serum), (iii) complement-dependent killing curves, (iv) double diffusion in gel (Ouchterlong), and (v) a new visual method for the detection of antigen-antibody reactions on glass slides coated with a thin film of indium metal. Our results indicate that the reactivity of the antisera, as assayed by the above methods, is significantly affected by the composition of the growth medium used for preparation of the antigen. In addition, it was possible to determine that the guinea pig serum-dependent killing of T960 was not affected by the presence of ammonium ion.

Animals↗
PubMed1975

Current theories of biological aging.

Several lines of evidence have led to the notion that biological aging occurs as a result of changes in the information-containing molecules either at the genetic or epigenetic level. The error theory, the redundant message theory, the codon restriction theory, and the transcriptional event theory represent the major current conceptualizations of biological aging as held by most gerontologists. The finding that cultured normal human and animal cells undergo a finite number of population doublings in vitro has provided new insights into age changes at the cellular level. The number of mitotic events that cultured normal animal cells can undergo appears to be inversely related to the age of the donor. A direct proportionality exists, however, between the mean maximum life-span of a species and the number of population doublings that their cultured embryonic cells will undergo. The several biochemical decrements known to occur prior to the cessation of mitotic activity in vitro are thought to herald those manifestations of senescence seen in the whole animal. Yet to be explained is how those cell classes such as the germ plasm and continuously propagable cancer cells escape from the inevitability of biological aging.

Aging↗
PubMed1975

Contributions of cytoplasmic factors to in vitro cellular senescence.

Mass populations of normal human lung fibroblasts were enucleated by centrifugation at greater than or equal to 25,000 g in 4 mug/ml cytochalasin B. The 1 per cent of cells that did not enucleate where rendered nonviable by treatment with mitomycin C. Whole cells were poisoned with a 99 per cent lethal dose of the sulfhydryl reagent iodoacetate. The washed cells were then mixed with the anucleate cytoplasms, fused with inactivated Sendai virus, and planted in rotenone for 20 hours. Whereas normal cells are able to survive this rotenone treatment, the 1 per cent surviving iodoacetate-treated cells cannot withstand this additional stress. However, iodoacetate treated cells that fuse to untreated cytoplasms receive sufficient amounts of active enzymes to allow them to survive. Since this selective system does not rely on using enzymatic mutants, it should permit the selection of hybrids between anucleate cytoplasms and any type of whole cell. Cytoplasmic hybrids were cultured in order to determine their proliferative capacity. The life-spans of cytoplasmic hybrids between young and old cells were compared to those of young/young and old/old controls. Cytoplasmic factors do not appear to control in vitro cellular senescence.

Cell Division↗
PubMed1974

Variation in the life-span of clones derived from human diploid cell strains.

The doubling potential of several hundred clones derived from WI-38 and WI-26 cell cultures has been determined. Clones were isolated at various population doubling levels (PDLs) during the finite in vitro life-span of the mass (uncloned) cultures. In all cases, there was a large variation in population doubling potential (or life-span) among the clones isolated from a single mass culture. When clones were isolated from mass cultures which had undergone eight or nine population doublings, only about 50% of the clones were capable of more than eight population doublings. This percentage was further reduced when clones were isolated from mass cultures at higher PDLs. Mass cultures appear to be composed of two subpopulation classes: one with a low population doubling potential, and the other with a higher population doubling potential. Nevertheless, the highest doubling potential observed in clones isolated from any single culture was about the same as the doubling potential of the mass culture from which single cells were taken.

Cell Count↗
PubMed1974

Growth of T-strain mycoplasmas in medium without added urea: effect of trace amounts of urea and of a urease inhibitor.

Urea is currently considered to be a requirement for the propagation of T-strain mycoplasmas. We report here the replication of T-strain 960 (ATCC 25023) in media prepared from dialyzed components with added putrescine and allantoin but without added urea, or in dialyzed medium containing small amounts of added urea. The least amount of urea which allowed growth in the medium without allantoin was above 10 mug/ml. The amount of urea estimated to contaminate the added allantoin or putrescine was 5 mug/ml or less, which is insufficient to support T-strain replication. T-strain 960 was grown in the presence of urea and the urease inhibitor acetohydroxamic acid AHA where the organisms multiplied at a slower rate in the presence of AHA than in its absence. Urea hydrolysis occurred with concomitant ammonia accumulation and pH increase in cultures with AHA added.

Allantoin↗
PubMed1974

Dialysis culture of T-strain mycoplasmas.

Using dialyzing cultures of T-strain mycoplasmas, it was possible to make some observations relevant to the growth and metabolism of these organisms which would not be possible in nondialyzing cultures due to growth inhibition of the organisms by elevated pH and increased ammonium ion concentration in media containing urea. The rate of ammonia accumulation was found to be related to the initial urea concentration in the medium and could not be accounted for by any change in the multiplication rate of the organisms. More ammonia was generated than could be accounted for by the added urea alone, suggesting that an ammonia-producing activity other than urease may be present in T-strain mycoplasmas. Titers above 10(7) color change units per ml were achieved in dialysis cultures of a T-strain mycoplasma in the presence of urea, and such titers were maintained for approximately 60 h during dialysis culture in the absence of added urea.

Ammonia↗