L-lysine catabolic process to acetyl-CoA via saccharopine

Definition

Target type: biologicalprocess

The chemical reactions and pathways resulting in the breakdown of L-lysine into other compounds, including acetyl-CoA, via the intermediate saccharopine. [GOC:mah, MetaCyc:LYSINE-DEG1-PWY]

L-lysine catabolism to acetyl-CoA via saccharopine is a complex metabolic pathway that involves the breakdown of the essential amino acid lysine into acetyl-CoA, a key metabolic intermediate. This pathway is primarily found in mammals and some bacteria. It involves a series of enzymatic reactions that convert lysine to α-aminoadipate, then to saccharopine, and finally to α-ketoadipate. The following steps are involved in this process:

1. **Lysine Deamination:** Lysine is first deaminated by the enzyme lysine-ketoglutarate reductase (LKR), also known as α-aminoadipate-semialdehyde synthase, to form α-aminoadipate-semialdehyde. In this reaction, lysine loses its amino group, and the co-substrate NADPH is oxidized to NADP+.
2. **Saccharopine Formation:** The α-aminoadipate-semialdehyde then reacts with α-ketoglutarate in a reductive amination catalyzed by the enzyme saccharopine dehydrogenase. This reaction forms saccharopine, a cyclic amino acid. The co-substrate NADPH is used as a reducing agent in this reaction.
3. **Saccharopine Cleavage:** Saccharopine is then cleaved by the enzyme saccharopine reductase to form α-ketoadipate and glutamate. This reaction requires NAD+ as a co-substrate and results in the reduction of NAD+ to NADH.
4. **α-Ketoadipate Decarboxylation:** The α-ketoadipate is then decarboxylated by the enzyme α-ketoadipate decarboxylase to form glutaryl-CoA. This reaction releases carbon dioxide.
5. **Glutaryl-CoA Metabolism:** Glutaryl-CoA is further metabolized through a series of enzymatic reactions, ultimately yielding acetyl-CoA and succinyl-CoA, both of which are important intermediates in the citric acid cycle.

The L-lysine catabolic process to acetyl-CoA via saccharopine pathway plays a crucial role in lysine metabolism and provides a mechanism for generating acetyl-CoA, which is a vital energy source for many cellular processes. It also contributes to the biosynthesis of other essential molecules such as glutamate and succinyl-CoA.'
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Proteins (1)

Compounds (3)