Cells can also convert α-keto acids into amino acids, but...

Cells can also convert $\alpha$ -keto acids into amino acids, but because the reagents organic chemists use for this reaction are not available in cells, they carry out this reaction by a different mechanism (Section 24.14 ). a. What amino acid is obtained from the reductive amination of each of the following metabolic intermediates in a cell by reductive amination? b. What amino acids are obtained from the same metabolic intermediates when the amino acids are synthesized in the laboratory?

Cells can also convert $\alpha$ -keto acids into amino acids, but because the reagents organic chemists use for this reaction are not available in cells, they carry out this reaction by a different mechanism (Section 24.14 ).
a. What amino acid is obtained from the reductive amination of each of the following metabolic intermediates in a cell by reductive amination?
b. What amino acids are obtained from the same metabolic intermediates when the amino acids are synthesized in the laboratory?

Key Concepts

Reductive Amination

Reductive amination is a chemical process that converts carbonyl compounds, such as alpha?keto acids, into amines through the reaction with ammonia (or an amine) in the presence of a reducing agent. In biochemical pathways, enzymes catalyze this process under mild conditions using cofactors like NADH or NADPH, whereas laboratory methods typically employ chemical reducing agents that are not available in cellular environments.

Alpha-Keto Acids

Alpha-keto acids are organic compounds characterized by the presence of a keto group adjacent to the carboxylic acid group. They play a central role in metabolism as intermediates in pathways such as the citric acid cycle, and serve as precursors for the biosynthesis of amino acids through reactions like reductive amination.

Enzymatic vs. Chemical Synthesis Mechanisms

The mechanisms used by cells and by chemists to synthesize amino acids from alpha-keto acids differ significantly. Cellular synthesis relies on enzyme-catalyzed reactions that are highly specific and occur under physiological conditions, whereas chemical synthesis in the laboratory employs reagents and conditions tailored for synthetic efficiency, often leading to differences in reaction intermediates, stereochemistry, and overall reaction pathways.

Metabolic Intermediates

Metabolic intermediates are compounds that are part of larger biochemical pathways and serve as substrates for various enzymatic reactions. In the context of amino acid biosynthesis, intermediates like certain alpha-keto acids are central because they can be easily converted into amino acids through processes such as reductive amination, linking metabolism with the synthesis of essential biomolecules.

Transcript

00:02 Okay, this being a two -part question, it's important to know which, what exactly each part is asking.

00:10 So with part a, they want to know the products, what are the amino acid products of a reductive amination.

00:32 Now, the general mechanism looks like this.

00:48 So you have your carboxylic acid.

00:57 Okay.

01:00 And then you're going to go ahead and treat it with xs, which i'm going to short -handed as xs, not extra small.

01:12 So xs, ammonia, and trace amounts of acid.

01:23 Okay.

01:23 And then you're going to follow that with h2 pdc.

01:32 Okay.

01:34 And with that alone, we get our amino acid.

01:47 And i will redraw, change the colors for the changes to see.

01:57 Okay.

01:58 So we see when we treat carboxyic acid with excess ammonia and trace and then follow that up with h2pdc, we get our amino acid skeleton.

02:10 Now we have to figure out what pyruvic acid, oxalacetate, and alpha -kidogluterate look like under this, and the products they form.

02:28 So let's go ahead and draw them.

02:34 So this is hyrubate or pyruvic acid if we scroll down to mix in space we have acolycate which i will agree the as o a a acetyte and then let me just scroll down a little bit more to fit in our alpha keto glutrate so alpha geogluterate okay now we the key thing about this reaction is that everything happens at once, right? so the ammonium can only attack, ammonia can only attack from one side.

03:52 That's key.

03:53 The ammonia can only attack from one side.

03:57 So because of that, what ends up happening is we get this right here, should be like that.

04:14 You know oxygen there.

04:16 Okay, so because of that, we get one product, which is l.

04:22 Al -alanine.

04:25 The l -alanine looks like this.

04:36 Nh -l -rondi group.

04:40 So that's our l -alanine.

04:41 Okay.

04:43 Similarly, that same mechanism gets applied.

04:47 So because of that, we get this is our product.