Biomedical subjects

Dagmar Müller

Publications and source records attributed to Dagmar Müller.

6 recordsLinked to original sources

PubMed2006

Temporal grouping affects the automatic processing of deviant sounds.

The present study investigates the influence of auditory temporal grouping on automatic sound processing. We compared the mismatch negativity (MMN) event-related potential elicited by successive deviant tones in a condition in which sounds were organized in tone pairs with respective MMN obtained in a non-paired sequence. When successive deviants belonged to different tone pairs the second deviant elicited a higher MMN amplitude than the corresponding deviant in the non-paired condition. Moreover, this temporal grouping had immediate effects on the extraction of rules as revealed by the finding that first and single deviants at the second position of a tone pair elicited larger MMNs than corresponding deviants in the non-paired condition or first and single deviants at the first position of a tone pair. Results demonstrate that auditory objects generated by temporal proximity are treated as relatively encapsulated units and that automatic deviance-detection may rely on multiple hierarchically organized representations of sound sequences.

Adult↗

PubMed2005

Deviance-repetition effects as a function of stimulus feature, feature value variation, and timing: a mismatch negativity study.

The human auditory pre-attentive change detection system, indicated by the mismatch negativity component (MMN) of the event-related brain potential is known to be sensitive for the successive presentation of tones deviating in frequency. The present study investigated deviance-repetition effects as a function of stimulus feature, feature value variation, and stimulus-onset asynchrony (SOA). For succession of frequency and location deviants carrying the same feature value, MMN elicited by the second deviant was reduced significantly. The reduction of MMN amplitude was markedly smaller, if the second of two successive deviants carries a different feature value, as compared with same feature value deviants. The variation of SOA across the temporal window of integration did not influence the deviance-repetition effects. We suggest that the pre-attentive change-detection system evaluates the informational content of the succession of deviants enabling an effective scanning of the auditory environment for potentially relevant events.

Adult↗

PubMed2005

Auditory streaming affects the processing of successive deviant and standard sounds.

This study investigated the temporal relation between two early mechanisms of auditory information processing: the segregation of the auditory input into streams and the automatic deviance detection indicated by the mismatch negativity (MMN). To address this question the processing of successive deviant and standard tones within streaming and nonstreaming conditions was analyzed. In the streaming condition the amplitude reduction of MMN elicited by the second of two successive deviants was found to be smaller for successive deviants presented in different than in same streams. No corresponding MMN differences were obtained in a nonstreaming condition. These results demonstrate that stream segregation precedes deviance detection. Moreover, modulations of the N1 amplitudes elicited by successive standard tones in the streaming condition demonstrate that not only deviance-related processing but even initial sound processing is affected by streaming.

Acoustic Stimulation↗

PubMed2003

Sit-and-wait strategies in dynamic visual search.

The role of memory in visual search has lately become a controversial issue. Horowitz and Wolfe (1998) observed that performance in a visual search task was little affected by whether the stimuli were static or randomly relocated every 111 ms. Because a memory-based mechanism, such as inhibition of return, would be of no use in the dynamic condition, Horowitz and Wolfe concluded that memory is likewise not involved in the static condition. However, Horowitz and Wolfe could not effectively rule out the possibility that observers adopted a different strategy in the dynamic condition than in the static condition. That is, in the dynamic condition observers may have attended to a subregion of the display and waited for the target to appear there (sit-and-wait strategy). This hypothesis is supported by experimental data showing that performance in their dynamic condition does not differ from performance in another dynamic condition in which observers are forced to adopt a sit-and-wait strategy by being presented with a limited region of the display only.

Adult↗

PubMed2002

Degradation of aromatics and chloroaromatics by Pseudomonas sp. strain B13: purification and characterization of 3-oxoadipate:succinyl-coenzyme A (CoA) transferase and 3-oxoadipyl-CoA thiolase.

The degradation of 3-oxoadipate in Pseudomonas sp. strain B13 was investigated and was shown to proceed through 3-oxoadipyl-coenzyme A (CoA) to give acetyl-CoA and succinyl-CoA. 3-Oxoadipate:succinyl-CoA transferase of strain B13 was purified by heat treatment and chromatography on phenyl-Sepharose, Mono-Q, and Superose 6 gels. Estimation of the native molecular mass gave a value of 115,000 +/- 5,000 Da with a Superose 12 column. Polyacrylamide gel electrophoresis under denaturing conditions resulted in two distinct bands of equal intensities. The subunit A and B values were 32,900 and 27,000 Da. Therefore it can be assumed that the enzyme is a heterotetramer of the type A2B2 with a molecular mass of 120,000 Da. The N-terminal amino acid sequences of both subunits are as follows: subunit A, AELLTLREAVERFVNDGTVALEGFTHLIPT; subunit B, SAYSTNEMMTVAAARRLKNGAVVFV. The pH optimum was 8.4. Km values were 0.4 and 0.2 mM for 3-oxoadipate and succinyl-CoA, respectively. Reversibility of the reaction with succinate was shown. The transferase of strain B13 failed to convert 2-chloro- and 2-methyl-3-oxoadipate. Some activity was observed with 4-methyl-3-oxoadipate. Even 2-oxoadipate and 3-oxoglutarate were shown to function as poor substrates of the transferase. 3-oxoadipyl-CoA thiolase was purified by chromatography on DEAE-Sepharose, blue 3GA, and reactive brown-agarose. Estimation of the native molecular mass gave 162,000 +/- 5,000 Da with a Superose 6 column. The molecular mass of the subunit of the denatured protein, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 42 kDa. On the basis of these results, 3-oxoadipyl-CoA thiolase should be a tetramer of the type A4. The N-terminal amino acid sequence of 3-oxoadipyl-CoA thiolase was determined to be SREVYI-DAVRTPIGRFG. The pH optimum was 7.8. Km values were 0.15 and 0.01 mM for 3-oxoadipyl-CoA and CoA, respectively. Sequence analysis of the thiolase terminus revealed high percentages of identity (70 to 85%) with thiolases of different functions. The N termini of the transferase subunits showed about 30 to 35% identical amino acids with the glutaconate-CoA transferase of an anaerobic bacterium but only an identity of 25% with the respective transferases of aromatic compound-degrading organisms was found.

Acetyl-CoA C-Acyltransferase↗

PubMed1999

The mycelium-associated Streptomyces reticuli catalase-peroxidase, its gene and regulation by FurS.

During early stages of growth, Streptomyces reticuli synthesizes a hyphae-associated, haem-containing enzyme which exhibits catalase and peroxidase activities with broad substrate specificity (CpeB). The purified dimeric enzyme (160 kDa) consists of two identical subunits. Using anti-CpeB antibodies and an expression- as well as a mini-library, the corresponding cpeB gene was identified and sequenced. It encodes a protein of 740 aa with a molecular mass of 81.3 kDa. The deduced protein shares the highest level of amino acid identity with KatG from Caulobacter crescentus and Mycobacterium tuberculosis, and PerA from Bacillus stearothermophilus. Streptomyces lividans transformants carrying cpeB and the upstream-located furS gene with its regulatory region on the bifunctional vector pWHM3 produced low or enhanced levels of CpeB in the presence or absence of Fe ions, respectively. An in-frame deletion of the major part of furS induces increased CpeB synthesis. The data imply that FurS regulates the transcription of cpeB. The deduced FurS protein is rich in histidine residues, contains a putative N-terminally situated helix-turn-helix motif and has a molecular mass of 15.1 kDa. It shares only 29% amino acid identity with the Escherichia coli ferric uptake regulator (Fur) protein, but about 64% with FurA deduced from the genomic sequences of several mycobacteria. The predicted secondary structures of FurS and FurA are highly similar and considerably divergent from those of the E. coli Fur. In contrast to some Gram-negative bacteria, within several mycobacteria an intact furA gene or a furA pseudogene is upstream of a catalase-peroxidase (katG) gene predicted to encode a functional or a non-functional (Mycobacterium leprae) enzyme. Thus the data obtained for Streptomyces reticuli are expected to serve as an additional model to elucidate the regulation of mycobacterial catalase-peroxidase genes.

Amino Acid Sequence↗