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|標題:||Identification of essential histidine residues in a recombinant alpha-amylase of thermophilic and alkaliphilic Bacillus sp strain TS-23||作者:||Chang, C.T.
|關鍵字:||alpha-amylase;Bacillus sp TS-23;histidine;site-directed mutagenesis;amino-acid-sequence;nucleotide-sequence;cyclodextrin;glycosyltransferase;binding-site;enzymatic-properties;escherichia-coli;human salivary;gene;calcium;enzymes||Project:||Extremophiles||期刊/報告no：:||Extremophiles, Volume 7, Issue 6, Page(s) 505-509.||摘要:||
To understand the structure-function relationships of a truncated Bacillus sp. strain TS-23 alpha-amylase, each of His-137, His-191, His-239, His-269, His-305, His-323, His-361, His-436, and His-475 was replaced with leucine. The molecular masses of the purified wild-type and mutant enzymes were approximately 54 kDa. The specific activity of His323Leu and His436Leu was decreased by more than 52%, while His239Leu, His305Leu, and His475Leu showed activity similar to that of the wild-type enzyme. As compared with the wild-type enzyme, His323Leu and His436Leu exhibited a 62% decrease in the value of k(cat)/K-m. Alterations in His-191, His-239, His-305, and His-475 did not cause a significant change in the K-m or k(cat) values. At 70degreesC, a decreased half-life was observed in His436Leu. These results indicate that His-137, His-269, and His-361 of Bacillus sp. strain TS-23 alpha-amylase are important for proper catalytic activity and that His-436 may contribute to the thermostability of the enzyme.
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