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The Biochemistry of Yeast Threonine Deaminase
Author(s) -
Holzer H.,
Boll M.,
Cennamo C.
Publication year - 1964
Publication title -
angewandte chemie international edition in english
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 0570-0833
DOI - 10.1002/anie.196401011
Subject(s) - threonine , biochemistry , isoleucine , valine , enzyme , chemistry , leucine , pyridoxal , yeast , escherichia coli , pyridoxal phosphate , amino acid synthesis , biology , amino acid , cofactor , serine , gene , lysine
An optical assay, according to Warburg, for measuring the activity of the enzyme threonine deaminase (threonine → α‐ketobutyrate + NH + 4 ) is described. Some of the properties of the enzyme from yeast have been studied using this assay. Pyridoxal phosphate and pyridoxamine phosphate stabilize the enzyme in the crude extract. Valine, leucine, and isoleucine, and to a lesser extent threonine, NH + 4 , and K+ protect the enzyme from inactivation when diluted with buffer. The enzyme is inhibited by isoleucine. The extend of the inhibition is dependent on the pH. Thus, in yeast, just as described for Escherichia coli by Umbarger, isoleucine exerts a control on its biosynthesis from threonine by means of a feed‐back mechanism, the extend of the control being related to the consumption of isoleucine in protein synthesis. NH + 4represses the biosynthesis of threonine deaminase. This mechanism regulates the threonine deaminase‐catalysed formation of NH + 4from threonine in accordance with the NH + 4 ‐requirements of the growing cell.