Genetical and physiological studies of lysine catabolism and implications for beta-lactam biosynthesis in streptomycetes.
Date
1990
Authors
Madduri, Krishnamurthy.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
Biochemical and genetic analyses of lysine catabolism have revealed the presence of diverse lysine catabolic pathways in streptomycetes. The $\alpha$-aminoadipate (AAA) pathway which generates a precursor, $\alpha$-aminoadipate, for $\beta$-lactam biosynthesis is present only in $\beta$-lactam producers and is a secondary metabolic pathway not necessary for growth under any known conditions. The cadaverine pathway is present in all actinomycetes tested and is used to catabolize lysine when needed as a nitrogen source. S. venezuelae has an additional minor pathway for assimilation of lysine via D-lysine, pipecolate and AAA.
The cadaverine pathway enzyme, cadaverine aminotransferase (CAT), is induced by its substrate and is strongly depressed by well-metabolized carbon sources such as glycerol and starch, and mildly by nitrogen sources such as glutamate. Lysine $\epsilon$-aminotransferase (LAT), the enzyme catalyzing the first step in the AAA pathway, is not induced by its substrate but is depressed by glycerol. There is a positive correlation between phosphate concentration and LAT activity.
The putative LAT gene is present in a cluster of genes encoding early enzymes governing $\beta$-lactam biosynthesis and is located between genes pcbC and cefE. In contrast, the cadaverine pathway genes are not adjacent to $\beta$-lactam biosynthesis genes. The two lysine catabolic pathways are apparently not interchangeable, consistent with the conclusion that the AAA pathway functions specifically in secondary metabolism. The sequence encoding LAT is present only in $\beta$-lactam producers; hence, the conversion of lysine to piperideine-6-carboxylate by LAT is the first step in $\beta$-lactam biosynthesis in Streptomyces.
Thesis (Ph.D.)--Dalhousie University (Canada), 1990.
The cadaverine pathway enzyme, cadaverine aminotransferase (CAT), is induced by its substrate and is strongly depressed by well-metabolized carbon sources such as glycerol and starch, and mildly by nitrogen sources such as glutamate. Lysine $\epsilon$-aminotransferase (LAT), the enzyme catalyzing the first step in the AAA pathway, is not induced by its substrate but is depressed by glycerol. There is a positive correlation between phosphate concentration and LAT activity.
The putative LAT gene is present in a cluster of genes encoding early enzymes governing $\beta$-lactam biosynthesis and is located between genes pcbC and cefE. In contrast, the cadaverine pathway genes are not adjacent to $\beta$-lactam biosynthesis genes. The two lysine catabolic pathways are apparently not interchangeable, consistent with the conclusion that the AAA pathway functions specifically in secondary metabolism. The sequence encoding LAT is present only in $\beta$-lactam producers; hence, the conversion of lysine to piperideine-6-carboxylate by LAT is the first step in $\beta$-lactam biosynthesis in Streptomyces.
Thesis (Ph.D.)--Dalhousie University (Canada), 1990.
Keywords
Biology, Microbiology.