Subject(s)
Dioxygenases , Escherichia coli/enzymology , Oxygenases/metabolism , Catalysis , Catechol 2,3-Dioxygenase , Chromosome Mapping , Chromosomes, Bacterial , Cloning, Molecular , Electron Spin Resonance Spectroscopy , Escherichia coli/genetics , Isomerism , Oxygenases/chemistry , Oxygenases/genetics , Phenylpropionates/metabolism , Recombinant Proteins/metabolism , Substrate SpecificityABSTRACT
The nucleotide sequence of the Escherichia coli mhpB gene, encoding 2,3-dihydroxyphenylpropionate 1,2-dioxygenase, was determined by sequencing of a 3.1-kb fragment of DNA from Kohara phage 139. The inferred amino acid sequence showed 58% sequence identity with the sequence of an extradiol dioxygenase, MpcI, from Alcaligenes eutrophus and 10 to 20% sequence identity with protocatechuate 4,5-dioxygenase from Pseudomonas paucimobilis, with 3,4-dihydroxyphenylacetate 2,3-dioxygenase from E. coli, and with human 3-hydroxyanthranilate dioxygenase. Sequence similarity between the N- and C-terminal halves of this new family of dioxygenases was detected, with conserved histidine residues in the N-terminal domain. A model is proposed to account for the relationship between this family of enzymes and other extradiol dioxygenases. The A. eutrophus MpcI enzyme was expressed in E. coli, purified, and characterized as a protein with a subunit size of 33.8 kDa. Purified MhpB and MpcI showed similar substrate specificities for a range of 3-substituted catechols, and evidence for essential histidine and cysteine residues in both enzymes was obtained.
Subject(s)
Alcaligenes/enzymology , Bacterial Proteins/genetics , Catechols/metabolism , Dioxygenases , Escherichia coli/enzymology , Oxygenases/genetics , Alcaligenes/genetics , Amino Acid Sequence , Bacterial Proteins/metabolism , Base Sequence , Catechol 2,3-Dioxygenase , Catechols/chemistry , DNA, Bacterial , Escherichia coli/genetics , Humans , Molecular Sequence Data , Oxygenases/metabolism , Sequence Homology, Amino AcidABSTRACT
Recent experimental research suggests an association between negative affect and potentiation of the human startle reflex, as well as enhancement of this effect among fearful compared to low fear subjects. In the present study, 32 undergraduates were selected for high or low total Fear Survey Schedule scores. Acoustic startle probes were presented while subjects received warned presentations of aversive and neutral photographic slides. High fear but not low fear subjects showed potentiated short-latency cardiac acceleration and blink magnitude, and reduced blink latency, during aversive compared to neutral slides. These results support the hypothesis that affective modulation of startle is enhanced among high fear compared to low fear subjects. Considered in the context of prior findings, the results suggest that this individual difference effect generalizes across psychophysiological components of the startle reflex and diverse procedures for manipulating affect.
