Regulation and structure of aspartokinase in the genusBacillus |
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Authors: | Henry Paulus |
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Institution: | (1) Department of Metabolic Regulation, Boston Biomedical Research Institute, 02114 Boston, Massachusetts, USA;(2) Department of Biological Chemistry, Harvard Medical School, 02115 Boston, Massachusetts, USA |
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Abstract: | The aspartate pathway of amino acid biosynthesis in bacteria serves as paradigm for the evolution of patterns of enzyme regulation
in response to specific physiological requirements. InBacillus species, the first step in the pathway is catalyzed by multiple forms of aspartokinase, which differ in their structure and
feedback regulation. One form of aspartokinase (V-type) functions primarily during cell growth, another form (S-type) during
sporulation. The V-type aspartokinase fromBacillus subtilis andBacillus polymyxa is discussed in some detail on account of its complex pattern of regulation by the pathway endproducts lysine and threonine
and its unusual subunit structure. The enzyme is composed of two dissimilar subunits, the smaller of which corresponds to
the carboxyl-terminal domain of the larger subunit. The coding sequence for the subunits ofBacillus subtilis aspartokinase has recently been cloned inEscherichia coli. The study of its structure and mode of expression has revealed that the two aspartokinase subunits are encoded by in-phase
overlapping genes. These unusual features of aspartokinase suggest that important aspects of the regulation of the aspartate
pathway are yet to be discovered. |
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Keywords: | Amino acid biosynthesis aspartokinase enzyme regulation Bacillus species allosteric control overlapping genes subunit structure |
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