Pathways

L-alanine is an essential component of proteins and peptidoglycan. The latter also contains about three molecules of D-alanine for every L-alanine. Only about 10 percent of the total alanine synthesized flows into peptidoglycan.There are at least 3 ways to begin the biosynthesis of alanine. The first method for alanine biosynthesis begins with L-cysteine produced from L-cysteine biosynthesis pathway. L-cysteine reacts with an [L-cysteine desulfurase] L-cysteine persulfide through a cysteine desulfurase resulting in a release of [L-cysteine desulfurase] l-cysteine persulfide and L-alanine. The second method starts with pyruvic acid reacting with L-glutamic acid through a glutamate-pyruvate aminotransferase resulting in a oxoglutaric acid and L-alanine. The third method starts with L-glutamic acid interacting with Alpha-ketoisovaleric acid through a valine transaminase resulting in an oxoglutaric acid and L-valine. L-valine reacts with pyruvic acid through a valine-pyruvate aminotransferase resulting Alpha-ketoisovaleric acid and L-alanine. This first step of the pathway, which can be catalyzed by either of two racemases (biosynthetic or catabolic), also serves an essential role in biosynthesis because its product, D-alanine, is an essential component of cell wall peptidoglycan (murein). D-alanine is metabolized by an ATP driven D-alanine ligase A and B resulting in D-alanyl-D-alanine. This product is incorporated into the peptidoglycan biosynthesis. L-alanine is metabolized with alanine racemase, either catabolic or metabolic resulting in a D-alanine. This compound reacts with water and a quinone through a D-amino acid dehydrogenase resulting in Pyruvic acid, hydroquinone and ammonium, thus entering the central metabolism and thereby can serve as a total source of carbon and energy. The role of the dadX racemase is degradative and dadX racemase can be induced by alanine and is subject to catabolite repression.

L-alanine is an essential component of proteins and peptidoglycan. The latter also contains about three molecules of D-alanine for every L-alanine. Only about 10 percent of the total alanine synthesized flows into peptidoglycan.There are at least 3 ways to begin the biosynthesis of alanine. The first method for alanine biosynthesis begins with L-cysteine produced from L-cysteine biosynthesis pathway. L-cysteine reacts with an [L-cysteine desulfurase] L-cysteine persulfide through a cysteine desulfurase resulting in a release of [L-cysteine desulfurase] l-cysteine persulfide and L-alanine. The second method starts with pyruvic acid reacting with L-glutamic acid through a glutamate-pyruvate aminotransferase resulting in a oxoglutaric acid and L-alanine. The third method starts with L-glutamic acid interacting with Alpha-ketoisovaleric acid through a valine transaminase resulting in an oxoglutaric acid and L-valine. L-valine reacts with pyruvic acid through a valine-pyruvate aminotransferase resulting Alpha-ketoisovaleric acid and L-alanine. This first step of the pathway, which can be catalyzed by either of two racemases (biosynthetic or catabolic), also serves an essential role in biosynthesis because its product, D-alanine, is an essential component of cell wall peptidoglycan (murein). D-alanine is metabolized by an ATP driven D-alanine ligase A and B resulting in D-alanyl-D-alanine. This product is incorporated into the peptidoglycan biosynthesis. L-alanine is metabolized with alanine racemase, either catabolic or metabolic resulting in a D-alanine. This compound reacts with water and a quinone through a D-amino acid dehydrogenase resulting in Pyruvic acid, hydroquinone and ammonium, thus entering the central metabolism and thereby can serve as a total source of carbon and energy. The role of the dadX racemase is degradative and dadX racemase can be induced by alanine and is subject to catabolite repression.

L-alanine metabolized from pyruvate and glutamate reacting through a Alanine aminotransferase resulting in the release of a oxoglutaric acid and a alanine. Alanine is degraded by alanine aminotransferase to form pyruvic acid. Meanwhile, oxoglutaric acid is converted to L-glutamic acid also by alanine aminotransferase. Pyruvate is transported into mitochondria for further metabolism.

L-arabinose enters E. coli unphosphorylated via a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH). Following entry, it is converted to L-ribulose-5-phosphate by an isomerase and kinase. L-ribulose-5-phosphate is then converted by an epimerase to the pentose phosphate pathway intermediate, D-xylulose-5-phosphate. D-xylulose-5-phosphate then enters metabolism pathways to become precursor metabolites, reducing power and metabolic energy.

L-arabinose enters E. coli unphosphorylated via a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH). Following entry, it is converted to L-ribulose-5-phosphate by an isomerase and kinase. L-ribulose-5-phosphate is then converted by an epimerase to the pentose phosphate pathway intermediate, D-xylulose-5-phosphate. D-xylulose-5-phosphate then enters metabolism pathways to become precursor metabolites, reducing power and metabolic energy.

L-arabinose enters E. coli unphosphorylated via a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH). Following entry, it is converted to L-ribulose-5-phosphate by an isomerase and kinase. L-ribulose-5-phosphate is then converted by an epimerase to the pentose phosphate pathway intermediate, D-xylulose-5-phosphate. D-xylulose-5-phosphate then enters metabolism pathways to become precursor metabolites, reducing power and metabolic energy.

L-arabinose enters E. coli unphosphorylated via a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH). Following entry, it is converted to L-ribulose-5-phosphate by an isomerase and kinase. L-ribulose-5-phosphate is then converted by an epimerase to the pentose phosphate pathway intermediate, D-xylulose-5-phosphate. D-xylulose-5-phosphate then enters metabolism pathways to become precursor metabolites, reducing power and metabolic energy.

L-arabinose enters E. coli unphosphorylated via a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH). Following entry, it is converted to L-ribulose-5-phosphate by an isomerase and kinase. L-ribulose-5-phosphate is then converted by an epimerase to the pentose phosphate pathway intermediate, D-xylulose-5-phosphate. D-xylulose-5-phosphate then enters metabolism pathways to become precursor metabolites, reducing power and metabolic energy.

L-arabinose enters E. coli unphosphorylated via a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH). Following entry, it is converted to L-ribulose-5-phosphate by an isomerase and kinase. L-ribulose-5-phosphate is then converted by an epimerase to the pentose phosphate pathway intermediate, D-xylulose-5-phosphate. D-xylulose-5-phosphate then enters metabolism pathways to become precursor metabolites, reducing power and metabolic energy.