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Biomedical subjects

L Hager

Publications and source records attributed to L Hager.

12 recordsLinked to original sources
PubMed1993

Method of recruiting subjects and performance on cognitive tests.

College students often serve as participants in psychological research. The effects of three methods of recruiting subjects for laboratory tests of attention and memory were assessed in a series of studies. The performance of students who received monetary incentives and the performance of students who received course-credit incentives were compared with the performance of students recruited from classes where research participation was a requirement. Monetary incentives resulted in slight, but significant, improvements in performance on tests of sustained attention and recognition memory. Course-credit incentives did not affect subjects' test performance. Test performance did not differ as a function of the time of the semester when studies were conducted. Recruitment issues pertinent to departmental subject pools are discussed.

Adolescent↗
PubMed1991

Are names ever mapped onto preexisting categories?

Support for Mervis's (1987) proposal that youngsters map new common nouns onto attribute cluster categories was obtained. In 3 studies, preschoolers interpreted a novel noun as if it designated a preexposed category. Experiment 3 included a group of adults who behaved similarly. Mapping was independent of the tendency to generalize according to shape. Neither age group mapped onto preexisting categories when making object similarity judgments, but preexposure did bias their naming of the objects' colors. Those who had examined sets containing 2 colors, both of which covaried with other bivalent dimensions, used more distinctive names for these hues than those preexposed to sets containing 6 colors, none of which covaried with bivalent dimensions.

Child, Preschool↗
PubMed1985

Conversion of alpha-amino acids and peptides to nitriles and aldehydes by bromoperoxidase.

Pure bromoperoxidase from the marine alga, Penicillus capitatus, converts alpha-amino acids and peptides to the corresponding decarboxylated nitriles and aldehydes in the presence of hydrogen peroxide and bromide ion. Thus, both valine and valylvaline are converted to isobutyronitrile and isobutyraldehyde while alanine is converted to acetonitrile and acetaldehyde. The reaction is nonstereospecific and can be catalyzed by bromoperoxidases obtained from different sources. Bromoperoxidase catalyzes the conversion of methoxytyrosine to p-methoxyphenylacetonitrile. This reaction is consistent with the involvement of bromoperoxidase in the formation of aeroplysinin-1, a brominated aromatic nitrile antibiotic produced by a marine sponge.

Aldehydes↗
PubMed1982

Crystallization and preliminary X-ray data for chloroperoxidase.

The enzyme chloroperoxidase from the fungus Caldariomyces fumago has been crystallized in a form suitable for detailed three-dimensional x-ray structure determination. Crystals grown from polyethylene glycol solutions display high resolution diffraction patterns indicating the orthorhombic space group C2221: a = 151.1 (3), b = 57.9 (4), c = 102.7 (9) A, V = 9 X 10(5) A3. A volume to mass ratio Vm = 2.8 A3/dalton for 8 molecules in the unit cell and a measured density of 1.35 g/cm3 suggest that the asymmetric unit contains a single chloroperoxidase molecule.

Animals↗
PubMed1980

Butyrate and related inhibitors of histone deacetylation block the induction of egg white genes by steroid hormones.

The short chain aliphatic acid salts, butyrate and propionate, are effective inhibitors of histone deacetylation in chick oviduct at 2--5 mM; they also prevent the hormonal induction of the ovalbumin and transferrin genes. The less potent deacetylase inhibitor isobutyrate is correspondingly less effective in blocking egg white mRNA induction; acetate has little effect at concentrations up to 15 mM. Butyrate does not appear to alter estrogen receptor binding in the nucleus, total RNA synthesis, or protein synthesis during the early hours of treatment when its specific effects on deacetylation and egg white gene transcription are observed. In addition to preventing the induction, butyrate also causes a rapid deinduction when added to preinduced cultures; ovalbumin and transferrin gene transcription decline with a half-life of 15--30 min. The effects of butyrate on egg white mRNA induction and deacetylation are completely reversible, and mRNA induction resumes within 1 hr after removal of butyrate from the medium. These results suggest that the modification of either histones or other unidentified regulatory proteins by acetylation may play a role in the mechanism of estrogen-mediated gene induction.

Acetylation↗
PubMed1976

Sequences related to immunoglobulin kappa chain messenger RNA in T cells.

We investigated by molecular hybridization whether T cells contain RNA sequences homologous to RNA which codes for immunoglobulin kappa-chain (k-chain). A radioactive probe of complementary DNA (cDNA) was prepared by transcription of purified k-chain mRNA from mouse myeloma MOPC-41 with reverse transcriptase (RNA-dependent-DNA nucleotidyltransferase) from avian myeloblastosis virus. The cDNA probably corresponded only to the constant region and 3'-terminus of k-chain mRNA. Kappa-chain cDNA was found to hybridize efficiently with RNA from both thymus cells and an established culture of thymoma cells. The thymus and thymoma cells contained 99.8% and 100% theta-positive cells, respectively. Quantitatively the average thymus T cell (thymus derived lymphocyte) contained about one half as much k-chain mRNA as the average spleen B cell ("bursa" dependent lymphocyte), whereas the thymoma cells contained only 1/33 as much. Control hybridizations of k-chain cDNA with myeloma and liver RNA support the conclusion that T cells in the thymus and in the thymoma cell line synthesize k-chain mRNA-like molecules. The thermal stability of hybrids of k-chain cDNA with RNA from spleen, thymus, thymoma, and another k-chain producing myeloma tumor was lower than that with MOPC-41 RNA. This finding may be due to the existence of several slightly different ck genes in the mouse as suggested by various control experiments.

B-Lymphocytes↗
PubMed1974

Simian virus 40 T antigen binds to DNA.

The T antigen of simian virus 40, which may play a role in the control of viral DNA replication, is recovered from nuclei of cells transformed by simian virus 40 in several forms sedimenting at different rates. The large molecular weight forms are converted to the smallest (5 S) form by high salt, suggesting that they differ in the degree of aggregation. All the forms of the antigen bind efficiently to double-stranded DNA-cellulose columns at pH 6.2 and low salt, and elute in two fractions: one at pH 8.0 and low salt, the other at pH 8.0 and high salt. The antigen has little affinity for single-stranded DNA.

Animals↗