PubMed Health⌕ Search

Biomedical subjects

C Chang

Publications and source records attributed to C Chang.

At least 451 records · Page 25Linked to original sources
PubMed1977

Structural transition in chromatin induced by ions in solution.

Structural transition in chromatin was measured as a function of counter ions in solution (NaCl or MgCl(2)) and of histones bound on the DNA. The addition of counter ions to aqueous solutions of chromatin, partially dehistonized chromatin, and DNA caused a drastic reduction in viscosity and a significant increase in sedimentation coefficient. Transitions occurred primarily at about 2 x 10(-3) M NaCl and 1 x 10(-5) M MgCl(2) and are interpreted as a change in structure of chromatin induced by tight binding of cations (Na(+) or Mg(++)) to DNA, either free or bound by histones, and is an intrinsic property of DNA rather than of the type of histone bound. At a given ionic condition, removal of histone H1 from chromatin had only a minor effect on the hydrodynamic properties of chromatin while removal of other histones caused a drastic change in these properties. An increase in the sedimentation coefficient of DNA was observed also for protamine. DNA complexes wherein the bound protein contains only unordered coil rather than the alpha-helices found in histones.

Animals↗
PubMed1977

Expression and thermal stability of simian virus 40 tumor-specific transplantation antigen and tumor antigen in wild type- and tsA mutant-transformed cells.

We have explored aspects of a suggested relationship between the expression of simian virus 40 tumor-specific transplantation antigen (TSTA) and tumor antigen (TA). A unique rat embryo cell line transformed by a temperature-sensitive A mutant that loses TA during exposure to the nonpermissive temperature (A28-RE) was found to lose TSTA. On the other hand, a typical control tsA-transformed cell line (A239-MB) expressed both TA and TSTA at the non-permissive temperature. TA in lysates obtained from A239-MB cells was found to be three to four times more thermolabile by covwt-mb) when incubated at either 33 or 40 degrees C. These data complement previous reports using TA from lytic infection and are consistent with the suggestion that TA is virus encoded. In contrast to TA, which even in wild-type-transformed cells was completely destroyed in less than 10 min at 50 degrees C, TSTA, assayed in vivo by tumor rejection, and tumor-specific surface antigen(s) TSSA) defined by an in vitro cytolytic assay, were thermostabile. Even after 24 h of incubation of extracts of 50 degrees C, high levels of TSTA and TSSA activity were present. Since these surface antigens when obtained from cells transformed by tsA mutants were also thermostabile, they could not be distinguished from the wild-type antigens. These results (i) indicate a coordinate expression of TA and TSTA in transformed cells; (ii) confirm that TA is virus encoded; and (iii) confirm that tha antigenic and immunogenic determinants that characterize TA and TSTA activities are distinct. However, the possibility that TSTA, like TA, is of viral rather than cellular origin is not excluded.

Animals↗
PubMed1977

Expression of tumor-specific transplantation antigen in cell lines transformed by wild-type of tsA mutant simian virus 40.

The simian virus 40-induced tumor-specific surface antigen(s) (TSSA) and tumor-specific transplantation antigen(s) (TSTA)were detected in cells transformed by wild-type or temperature-sensitive mutant simian virus 40 by an antibody-mediated cytolytic assay for TSSA and an immunization test for TSTA. Cells transformed by tsA mutants, which lose their transformed phenotype when grown at nonpermissive temperatures, nonetheless do express TSSA and TSTA as well as T-antigen at both temperatures.

Animals↗
PubMed1976

Adjuvant nitrosourea therapy for glioblastoma.

An attempt was made to evaluate the potential advantages of chemotherapy in the treatment of 62 patients with glioblastoma. Twenty-four of the 62 patients received adjuvant nitrosourea chemotherapy with carmustine (BCNU), lomustine (CCNU), or semustine (methyl CCCNU) in addition to surgery and radiotherapy. Thirty-three of the 62 patients were involved in a controlled, prospective, randomly allocated study. Quality or quantity of survival was not prolonged in patients who received chemotherapy. Age greater than 64 years, a severe postoperative neurological deficit, or the onset of symptoms less than 12 months prior to surgery were associated with a worse prognosis. The valid evaluation of the effect of a form of treatment on survival in patients with glioblastoma is contingent on the regorous avoidance of preselected factors that may predispose the treated group to a more favorable prognosis.

Adolescent↗
PubMed1976

Family planning in a Chinese-American population.

Among 26 American-born women of Chinese ancestry, 43 Chinese immigrant women who had lived in San Francisco longer than 5 years, and 199 who had immigrated within the last 5 years, fewer than 39% practiced contraception. Oral contraception was used by significantly more of the American-born than of the other two categories of women. Condom or foam was relied upon by sizeable percentages of each immigrant group. Eleven percent of each immigrant group, and 13.3% of the American-born women were sterilized. The only users of an intrauterine device were 3.7% of the immunigrants who had lived in the United States longer than 5 years.

California↗
PubMed1976

Comparative physiologic dispositions of 5-fluoro-2'-deoxyuridine and 5-fluorouracil in mice bearing solid L1210 lymphocytic leukemia.

The physiologic disposition of 5-fluoro-2'-deoxyuridine (FUdR) and its metabolites, in particular the postulated active metabolite, 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP), has been studied in BDF1 mice bearing 6-day solid L1210 lymphocytic leukemia between 2 and 72 hours after a single iv dose of 14C-2-FUdR at 380 or 760 mg/kg (400-1300 microcuries/kg). FUdR itself was rapidly eliminated from tissues by urinary excretion and metabolism. However, its metabolites, including 5-fluorouracil (FU), persisted for 72 hours in the acid-soluble and -insoluble fractions of tissues. In tumor and small intestine, 60% of the 0- and 72-hour exposure to FdUMP, based on the area under the concentration-time curve, occurred between 24 and 72 hours after dosing. The results are compared with the physiologic disposition of FU after administration at 200 mg/kg iv which is an equimolar dose to FUdR at 380 mg/kg and approximately equitoxic to FUdR at 760 mg/kg. The molar concentrations of total drug equivalents, and of FU itself, after FUdR at 760 mg/kg were comparable to those after FU. However, the concentrations of FdUMP were lower than after FU, whereas the concentrations of drug equivalents incorporated into the acid-insoluble fraction, which includes equivalents incorporated into RNA, were generally higher than after FU. These data are correlated with the comparative antitumor effects and toxicity in mice of the fluorinated pyrimidines and with their clinical effectiveness.

Animals↗
PubMed1975

Carbon-13 magnetic resonance spectroscopy of drugs. Sulfonamides.

The natural abundance 13C magnetic resonance spectra of a series of sulfonamide drugs(sulfanilamide, sulfaguanidine,sulfathiazole, sulfasuxidine, sulfadiazine, sulfamerazine, sulfamethiazine, and sulfapyridine) have been determined at 25.15 MHz employing the pulse Fourier transform technique. The chemical shefts have been assigned with the aid of off-resonance and selective proton decoupling techniques, as well as by long-range carbon-13 proton coupling patterns.

Chemical Phenomena↗
PubMed1975

Longitudinal measurements of blood volume and essential body mass in human subjects.

Repeated determinations of blood volume and body density were made on 34 Chinese subjects (28 men and 6 women) in Taiwan over a period of 12 yr, as the mean age increased from 31 to 43 yr. Essential body mass calculated from body density and body weight showed no significant change over the 12-yr period. Changes in body weight (mean gain equals 6.0 kg) were attributable to alterations in adipose tissue weight, the density of which was found to be 0.948 g/cm3. In two-thirds of the subjects the second blood volume increased by more than 5% over the first determination, and the mean blood volume for all subjects increased by 7.5% (P less than 0.01). Correlation of the blood volume data with the findings on essential body mass and adipose tissue mass suggests that blood content per unit tissue mass increased in the second determination. This interpretation is supported by the increase in nutrient availability in Taiwan over the 12-yr period, and it may explain the lack of blood volume increase in an earlier longitudinal study on American subjects with stable nutrient availability.

Adult↗
PubMed1975

Longitudinal studies on adipose tissue and its distribution in human subjects.

On 27 men and 6 women, total body density and 10 skinfolds were measured 12 yr apart, with the mean age increasing from 31 to 43 yr. The increase in skinfold thickness was found to be related to the increase in total body adiposity, calculated from hydrostatic weighing. The external adipose tissue was calculated from the mean skinfold thickness and body surface area. Variations in total adiposity among the population studied as well as changes in total adiposity with age showed a characteristic distribution with approximately two-thirds on the surface and one-third in the interior. The essential body mass or total adipose mass determined by hydrostatic weighing was compared with the values obtained by water-immersion volumetry, total body potassium counting, and skinfold measurements. Teh volumetric and skinfold determinations gave better estimates of these parameters than total body potassium counting.

Adipose Tissue↗