Severity: Warning
Message: file_get_contents(https://...@pubfacts.com&api_key=b8daa3ad693db53b1410957c26c9a51b4908&a=1): Failed to open stream: HTTP request failed! HTTP/1.1 429 Too Many Requests
Filename: helpers/my_audit_helper.php
Line Number: 176
Backtrace:
File: /var/www/html/application/helpers/my_audit_helper.php
Line: 176
Function: file_get_contents
File: /var/www/html/application/helpers/my_audit_helper.php
Line: 250
Function: simplexml_load_file_from_url
File: /var/www/html/application/helpers/my_audit_helper.php
Line: 1034
Function: getPubMedXML
File: /var/www/html/application/helpers/my_audit_helper.php
Line: 3152
Function: GetPubMedArticleOutput_2016
File: /var/www/html/application/controllers/Detail.php
Line: 575
Function: pubMedSearch_Global
File: /var/www/html/application/controllers/Detail.php
Line: 489
Function: pubMedGetRelatedKeyword
File: /var/www/html/index.php
Line: 316
Function: require_once
A unique enzyme with some properties favorable for the synthesis of D-amino acid-containing peptides has been purified from the culture broth of Saccharothrix sp. AS-2. The purification steps included ammonium sulfate fractionation, chromatographies on CM-Toyopearl 650M and ProtEx Butyl, and sucrose density-gradient isoelectric focusing. The enzyme, consisting of four subunits of 56 kDa, showed its maximum transfer activity at around pH 8.2 and 35 degrees C, and had an isoelectric point of 5.8. The enzyme yielded homooligomers from methyl esters of D-Asp(OMe), D-Met, D-Phe, D-Trp, D-Tyr, and L-Glu(OMe), but showed no hydrolytic activity toward any of the D- or L-amino acid methyl esters tested. The homooligomers were not formed from the corresponding free amino acids. The reaction of Ac-D-Phe-OMe with DL-Ala-NH(2), DL-Leu-NH(2), DL-Phe-NH(2), or DL-Trp-NH(2) was effectively catalyzed by the enzyme, both the DD- and DL-stereoisomers of the expected N-acetyldipeptide being yielded. The resulting dipeptides remained unhydrolyzed even after 48 h incubation. Also, it showed no detectable hydrolytic activity toward casein, diastereomers of diAla, diMet, and diPhe, D-/L-amino acid amides, or D-/L-amino acid p-nitroanilides, indicating that the enzyme had no peptidase activity leading to secondary hydrolysis of the growing peptide. The enzyme activity was strongly depressed by phenylmethanesulfonyl fluoride, but not by penicillin G or ampicillin, suggesting that the protein is a serine enzyme lacking penicillin-binding ability. These observations lead us to the conclusion that the enzyme from Saccharothrix sp. AS-2 characterized in this study is a new type of aminoacyltransferase with an amino acid ester as the acyl donor, and has potential utility as a catalyst for the synthesis of D-amino acid-containing peptides.
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Source |
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http://dx.doi.org/10.1093/oxfordjournals.jbchem.a003095 | DOI Listing |
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