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Biomedical subjects

C D Green

Publications and source records attributed to C D Green.

At least 55 records · Page 3Linked to original sources
PubMed1976

Characterization of polysomes from Xenopus liver synthesizing vitellogenin and translation of vitellogenin and albumin messenger RNA's in vitro.

1. Conditions are described for the isolation of polysomes from the liver of Xenopus laevis. The method involves homogenization of liver in 0.2 M Tris-HCl pH 8.5, treatment with 2% Triton X-100 and subsequent sucrose density gradient fractionation of polysomes from a 10000 X g supernatant. 2. Vitellogenin synthesis was induced in male Xenopus liver by oestradiol treatment. Polysomes were isolated and vitellogenin-synthesizing polysomes characterized by their association with monospecific 125 I-labelled rabbit anti-vitellogenin antibody and by reaction with rabbit anti-vitellogenin immunoglobulins followed by indirect immunoprecipitation with goat anti-rabbit antibody. 3. Changes in liver polysome content following oestrogen treatment of male Xenopus are correlated with the appearance of vitellogenin synthesis using an organ culture assay. 4. RNA extracted from livers of oestradiol-treated male Xenopus and from purified polysomes is shown to code for the synthesis of vitellogenin-specific immunoprecipitable polypeptides in a rabbit reticulocyte cell-free protein-synthesizing system, a major component having a molecular weight of 210000. Xanopus liver RNA is also shown to code for the synthesis of an albumin-specific immunoprecipitable polypeptide of 74000 molecular-weight which coelectrophoresed with Xenopus albumin.

Albumins↗
PubMed1976

Direct induction by estradiol on vitellogenin synthesis in organ cultures of male Xenopus laevis liver.

Organ cultures of liver from untreated male Xenopus respond to 17 beta-estradiol in the culture medium by synthesizing and secreting the yolk protein precursor vitellogenin. Vitellogenin synthesis, as a primary response, is first detectable on the fourth day of culture, and comprises up to 12% of the protein synthesized on the eighth day. Estradiol is required during the lag period of 4 days. Tissue from male Xenopus injected with 1 mg of estradiol 30 days before the start of culture responds more rapidly and to a greater extent to estradiol in the medium than tissue from uninjected males. During such a secondary response, vitellogenin is first detectable in the medium on the second day of culture, and becomes up to 24% of the protein synthesized on day 6. The rate of amino acid incorporation into total protein also increases in response to estradiol, but the rate of synthesis of albumin decreases rapidly in culture whether or not estradiol is present, in both the primary and secondary responses. A maximal response is seen with 10(-8) M estradiol. Progesterone, testosterone, dexamethasone, and insulin neither induce vitellogenin synthesis in culture nor modify the response to estradiol. DNA synthesis inhibitors do not prevent the response to estradiol in vitro, suggesting that cell division is not required for the initial response leading to vitellogenin synthesis.

Albumins↗
PubMed1975

A comparison of methods of evaluating myocardial contractility.

An investigation was carried out in dogs to determine how the acceleration of blood in the aorta (dV/dt), as a new index of myocardial contractility compared with existing indices and how they correlated with each other. It was found that the indices derived from velocity and flow of blood, dV/dt max and dQ/dt max, and from intraventricular pressure, dP/dt max, correlate well with each other but there is less agreement between them and the reciprocal of the Pre-Ejection Period, l/PEP. The ratio dP/dt max divided by I.P. correlated well with dQ/dt max divided by I.Q. and dQ/dt max divided by Q. max but not so well with dV/dt max divided by I.V. (instantaneous velocity) of dV/dt max divided by V. max and the ratios dQ/DT DIVIDED BY I.Q. and dQ/dt divided by Q max as well as l/PEP. In view of the lack of agreement of quantitative definition of myocardial contractility, the ratio dV/dt divided by V. max would have several practical advantages as an indicator of the inotropic state of the heart; these are that the probe used to establish descending aortic blood velocity does not require calibration, and the signal can be obtained by a relatively non-invasive technique that is suitable for patient care and yet agrees with other established indices of myocardial contractility.

Animals↗
PubMed1975

Preparation of nematodes for scanning electron microscopy.

Nematodes from the orders Tlyenchida and Rhabditida were fixed and processed in several different ways for examination with the scanning electron microscope (SEM). Four processes produced good preparations of fixed nematodes. Drying from acetone was the simplest of these techniques and most useful for regions of the tylenchid nematodes supported by skeletal tissue. Critical point drying, a more complicated procedure, gave good preparations, but they required special care in processing. Nematodes infiltrated with glycerol and a conducting agent were the most life-like but were difficult to examine. Specimens infiltrated with an epoxy resin looked natural and this was the most promising process tried.

Animals↗
PubMed1973

Characterization of a feedback-resistant phosphoribosylpyrophosphate synthetase from cultured, mutagenized hepatoma cells that overproduce purines.

A clone of cells in which the regulation of purine metabolism is genetically altered was selected and isolated from chemically mutagenized HTC cells (a line of rat hepatoma cells in continuous culture). The clone, designated MAU V, was selected for increased ability to salvage exogenous purines by isolating it in medium containing methylmercaptopurine ribonucleoside, adenine, and uridine, in which medium wild-type cells cannot divide. We have characterized these cells as having an increased rate of de novo purine biosynthesis, apparently as the result of an altered phosphoribosylpyrophosphate (PRPP) synthetase. The altered enzyme has normal catalytic properties but an altered sensitivity to feedback inhibition by purine and pyrimidine nucleotides. The types of inhibitions (competitive and uncompetitive) exerted by AMP, ADP, and TDP on the wild-type enzyme have been maintained in the altered enzyme, but values for K(i) have been increased by factors of 10, 17.5, and 5, respectively. The specific catalytic activities of AMP: pyrophosphate phosphoribosyltransferase and IMP:pyrophosphate phosphoribosyltransferase are normal. The mutant cell may serve as a model for a specific human disease, one type of dominantly inherited overproduction hyperuricemia.

Adenosine Diphosphate↗