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Biomedical subjects

S Petry

Publications and source records attributed to S Petry.

6 recordsLinked to original sources
PubMed1992

A spacer-modified disaccharide as a photoaffinity reagent for the acceptor-binding area of bovine (1----4)-beta-D-galactosyltransferase: comparison of its acceptor properties with those of other 2-acetamido-2-deoxy-beta-D-glucopyranosides.

The spacer-modified disaccharide 1,10-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-azi-1,10- decanediol (10) that mimics the biantennary core heptasaccharide of N-glycoproteins has been synthesised. Compound 10 is an excellent acceptor in galactosyltransferase-catalysed galactosylation by UDP-galactose, is superior (7-8-fold) to analogues that have only one GlcNAc unit, and is an efficient photoaffinity reagent for galactosyltransferase. In the presence of UDP-Gal, no photoaffinity labelling by 10 takes place, which agrees with the mechanism of galactosyltransferase action.

Animals↗
PubMed1992

Spacer-modified trisaccharide glycosides that mimic the biantennary Asn-linked oligosaccharide acceptor of (1----4)-beta-D-galactosyltransferase and can be used as competitive inhibitors and for irreversible deactivation.

The biantennary spacer-modified trisaccharide glycoside methyl 3,6-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyloxyethyl)-alpha -D- mannopyranoside (5) was synthesised and used together with several 2-acylamino-2-deoxy-D-glucose derivatives in competition experiments with beta-D-galactosyltransferase. Compound 5 was an acceptor substrate (KM 0.18 mM) comparable to the biantennary core heptasaccharide of glycoproteins (KM 0.13 mM). Replacing the N-acetyl group by other N-acyl groups did not alter the kinetic parameters significantly. When the N-acyl group was iodoacetyl, the compound was an irreversible inhibitor.

Asparagine↗
PubMed1991

Evidence for independent processing of subjective contour brightness and sharpness.

Subjective contours have been of considerable interest because of their importance to theories and physiological models of form perception. In particular, they have recently been characterized as the result of magnocellular cortical processing. There is, however, a paucity of parametric data relating to basic psychophysical parameters in this field. Two experiments are reported in which the roles of subjective contour size, retinal eccentricity, and flicker rate in subjective contour salience were investigated. Eleven observers estimated subjective contour magnitude using an Ehrenstein configuration. Configurations ranging in size from 0.25 to 3 deg were presented to three retinal loci (fovea, 2 deg, and 4 deg) at flicker rates ranging from 5 to 15 Hz. Subjective contour brightness and distinctness were measured separately. Brightness was greatest at a subjective contour size of about 1.25 deg, at flicker rates of 5-7 Hz, and at 3 deg peripheral for all flicker rates and all but the smallest stimulus sizes. Distinctness decreased with eccentricity and flicker, but remained high at small diameters (thus implicating spatially sensitive mechanisms). Taken together, the results support a magnocellular processing of subjective contours with respect to brightness, but also suggest that there is a parvocellular contribution to subjective contour sharpness.

Adult↗
PubMed1979

Decrease in metacontrast masking following adaptation to flicker.

Selective adaptation was used to explore the characterisitcs of a metacontrast masking stimulus which contribute to its effectiveness in masking the test stimulus. Subjects adapted for 10 s to a configuration like the masking stimulus that was either continuously on or flickering. Following this they viewed a metacontrast presentation and estimated the brightness of the test stimulus. Prior adaptation to a continuously present stimulus did not appreciably affect metacontrast masking; however, masking was greatly reduced following adaptation to flickering stimuli. These results are consistent with recent models of metacontrast masking based on transient and sustained visual channels.

Adaptation, Ocular↗