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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 65 (1995), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The degradation of dynorphin-related peptides by the puromycin-sensitive aminopeptidase and aminopeptidase M was examined using these peptides as alternate substrate inhibitors. Ki determinations showed that both aminopeptidases exhibit a higher affinity for longer dynorphin-related peptides, i.e., Ki for dynorphin A-17 = 23–30 nM with the Ki increasing to 25–50 µM for the enkephalin pentapeptides. Binding appears dependent not only on peptide length, but also on its sequence. With aminopeptidase M, as the peptide size increases from five to 10 amino acids, kcat remains relatively constant; however, as the peptide size increases beyond a decapeptide, kcat decreases significantly. With the puromycin-sensitive aminopeptidase, similar results were obtained except that kcat was greatest for the pentapeptide. Thus, if one considers kcat/Km as the relevant kinetic constant for estimating in vivo peptide hydrolysis, these results are consistent with the involvement of aminopeptidase M and the puromycin-sensitive aminopeptidase in the degradation of extended dynorphin-related peptides.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Choline acetyltransferase (ChAT) is specifically expressed in Cholinergic neurons. To identify control mechanisms regulating the cell-specific expression of the gene encoding ChAT, transient expression of the luciferase gene driven by human ChAT gene 5’ flanking sequences was compared in cholinergic and noncholinergic cell lines. Analysis of the gene indicated the presence of two regulatory elements with selective silencing activity. These elements, located between nucleotides −2043 to −3347 and nucleotides −3347 to −6550, act cooperatively to repress promoter activity 〉 10-fold in a human adrenergic neuroblastoma cell line, SHSY5Y, and a human osteosarcoma cell line, 143 TK, while exhibiting less than a two-fold effect in Cholinergic cell lines. Deletion of either nucleotides −2043 to −3347 or nucleotides −3348 to −6550 reduced cell-specific repression by approximately half. Such differential repression appears to be responsible for the selective expression of the ChAT component of the Cholinergic phenotype.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 62 (1994), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: It is well known that the regulation of choline acetyltransferase (ChAT) activity under physiological and pathological conditions is important for the development and neuronal activities of cholinergic systems involved in many fundamental brain functions. This review focuses on recent progress in understanding the regulation of ChAT at the levels of both the protein and the mRNA. A deficiency in ChAT activity has been reported for neurodegenerative conditions such as Alzheimer's disease, amyotrophic lateral sclerosis, and schizophrenia. Although a major feature of ChAT regulation is likely to involve the spatial and temporal control of transcription, regulation of expression can also be at the level of RNA processing, transport/ translocation, turnover, or translation. In addition, there is increasing evidence that ChAT might be regulated at the posttranslational level by compartmentation and/or covalent modification, i.e., phosphorylation, as well as noncovalent modification (protein-protein interaction, etc.). Synaptic activity and the state of neuronal transmission may also involve the regulation of ChAT at different levels via both positive and negative feedback loops, as was demonstrated in the characterization of two ChAT mutant Drosophila strains. Clearly, identification of cholinergic-specific elements and the characterization of the trans-acting factors that bind to them represent an important area of future research. Equally important is research on the mechanisms governing ChAT as an enzymatic entity. The future should be an exciting time during which we look forward to the elucidation of the cholinergic signal and its regulation as well as the determination of the three-dimensional structure of the enzyme.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The choline acetyltransferase (ChAT) reaction involves the transfer of the acetyl group of acetyl-CoA to choline, in which an active site histidine is believed to act as a general acid/base catalyst. A comparison of the deduced amino acid sequences of the enzyme from Drosophila, pig, rat, and Caernohabditis elegans revealed three conserved histidines: Drosophila His268, His393, and His426. Each of these histidines was replaced by a leucine and a glutamine, and the kinetic properties of each of the recombinant mutant enzymes were determined. The mutations yielded active His268Leu-ChAT, HisZ68Gln-ChAT, and His393Gln-ChAT and inactive His393Leu-ChAT, His426Leu- ChAT, and His426Gln-ChAT. The kinetic constants Km(CoA), Km(acetyloholine). and Vmax were essentially the same for all of the active mutants. When the integrity of the CoASAc binding site was investigated in the inactive mutants, the data suggested that the binding site in His393Leu-ChAT is disrupted but conserved in His426Leu-ChAT and His426Gln- ChAT. These results suggest that His426 is an essential catalytic residue and could serve as an acid/base catalyst.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 51 (1988), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The amino acid sequence of 11 peptides generated from human placental choline acetyltransferase was compared to the corresponding amino acid sequences predicted from the nucleotide sequence of a recently cloned porcine choline acetyltransferase cDNA. These peptides, which were generated by cyanogen bromide cleavage or tryptic digestion, accounted for 23% of the amino acids in the enzyme. Of the 145 amino acids sequenced eight differed between the two species, yielding an identity of 94% over the regions sampled.Of the eight amino acids that differed six could represent single base changes in the DNA sequence. These findings demonstrate strong sequence similarity between porcine and human choline acetyltransferase and indicate that they are closely related evolutionarily.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: A cDNA for Drosophila choline acetyltransferase (EC 2.3.1.6; ChAT) was fused with a polyhistidine sequence and expressed in Escherichia coli. The recombinant enzyme was purified to a specific activity of 500 μmol/min/mg of protein using metal affinity chromatography and ion exchange chromatography. Kinetic properties of the recombinant enzyme did not differ significantly from those previously determined. Circular dichroism (CD) spectra revealed that the secondary structure of the enzyme is largely μ-helical. Intrinsic fluorescence spectra of the enzyme indicate that its tryptophan residues are buried. Neither CD nor fluorescence spectra changed significantly in the presence of substrates. The cysteine content of the recombinant Drosophila ChAT was determined to be 16 in the absence and 22 in the presence of 6 M guanidine hydrochloride. Finally, crystallization of recombinant Drosophila ChAT was achieved.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Enkephalin degradation in brain has been shown to be catalyzed, in part, by a membrane-bound puromycinsensitive aminopeptidase. A cytosolic puromycin-sensitive aminopeptidase with similar properties also has been described. The relationship between the soluble and membrane forms of the rat brain enzyme is investigated here. Both of these aminopeptidase forms were purified from rat brain and an antiserum was generated to the soluble enzyme. Each of the aminopeptidases is composed of a single polypeptide of molecular mass 100 kilodaltons as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and sizeexclusion chromatography. The antisoluble aminopeptidase antiserum reacts with both enzyme forms on immunoblots and inhibits both with nearly identical inhibition curves. The isoelectric points (pI = 5.0) of both forms were shown to be identical. N-terminal sequencing yielded a common sequence (P-E-K-R-P-F-E-R-L-P-T-E-V-S-P-I-N-Y) for both enzyme forms, and peptide mapping yielded 26 peptides that also appeared identical between the two enzyme forms. Studies on the nature of the association of the membrane enzyme form with the cell membrane suggest that this enzyme form does not represent the soluble form trapped during the enzyme preparation. It is suggested that the membrane form of the puromycin-sensitive aminopeptidase is identical to the soluble enzyme and that it associates with the membrane by interactions with other integral membrane proteins.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 64 (1995), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Choline acetyltransferase activity is barely detectable in a mutant pheochromocytoma PC12 cell line, A123.7, which is deficient in protein kinase A activity. Northern blot and polymerase chain reaction analyses showed that this mutant cell line has dramatically reduced levels of choline acetyltransferase mRNA, which correlates with the low level of enzyme activity. Transient transfection analysis was used to assess the functionality, in these cells, of an enhancer element and a cholinergic-specific repressor element derived from the human choline acetyltransferase gene. The results show that the enhancer element is inactive in the protein kinase A-deficient cell line. Cotransfection experiments with plasmids expressing the catalytic subunit of protein kinase A support this conclusion. These data indicate that protein kinase A regulates expression of the choline acetyltransferase gene at the transcriptional level by controlling the activity of an enhancer element.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Genomic clones of human and porcine choline acetyltransferase were obtained by screening genomic libraries with synthetic oligonucleotides. The human and porcine genes exhibit significant conservation of both their intron/exon structure and the nucleotide sequence in their 5’flanking regions. However, the two genes differ in several respects, including the absence of a “TATA” box in the human gene and differences in the position of the methionine start codon. Analysis of the promoter region of the two genes has led to the localization of an enhancer element that appears necessary for efficient transcription of the gene.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 51 (1988), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: An antiserum generated to the soluble form of the rat brain puromycin-sensitive enkephalin-degrading amino-peptidase was used to determine the tissue distribution of the soluble and membrane-associated forms of this enzyme. All tissues examined contained significant levels of the soluble enzyme form, with this enzyme accounting for 〉90% of the arylamidase activity in brain, heart, and skeletal muscle. Native gel electrophoresis coupled with activity staining as well as inhibition studies were used to confirm the presence of this enzyme in various tissues. Serum was found not to contain this particular aminopeptidase. In contrast to the results obtained with the soluble enzyme form, brain was the only tissue found to contain the membrane-associated enzyme form. Although all tissues contained membrane-associated aminopeptidase activity only the brain enzyme could be maintained in solution in the absence of detergent. In addition, the brain membrane-associated enzyme could be distinguished from the membrane-associated aminopeptidase activity in other tissues on the basis of its sensitivity to inhibition by puromycin.
    Type of Medium: Electronic Resource
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