{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Amino Acid Catabolism of Carbon Skeletons

Amino Acid Catabolism of Carbon Skeletons - Molecular...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Amino Acid Catabolism: Carbon Skeletons Copyright © 1999-2007 by Joyce J. Diwan. All rights reserved. Molecular Biochemistry II
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Amino Acid Carbon Skeletons Amino acids , when deaminated, yield α -keto acids that, directly or via additional reactions, feed into major metabolic pathways (e.g., Krebs Cycle). Amino acids are grouped into 2 classes, based on whether or not their carbon skeletons can be converted to glucose: glucogenic ketogenic .
Background image of page 2
Carbon skeletons of glucogenic amino acids are degraded to: pyruvate , or a 4-C or 5-C intermediate of Krebs Cycle . These are precursors for gluconeogenesis . Glucogenic amino acids are the major carbon source for gluconeogenesis when glucose levels are low. They can also be catabolized for energy , or converted to glycogen or fatty acids for energy storage .
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Carbon skeletons of ketogenic amino acids are degraded to: acetyl-CoA , or acetoacetate . Acetyl CoA, & its precursor acetoacetate, cannot yield net production of oxaloacetate, the gluconeogenesis precursor. For every 2-C acetyl residue entering Krebs Cycle, 2 C leave as CO 2 . Carbon skeletons of ketogenic amino acids can be catabolized for energy in Krebs Cycle, or converted to ketone bodies or fatty acids . They cannot be converted to glucose .
Background image of page 4
The 3-C α -keto acid pyruvate is produced from alanine, cysteine, glycine, serine, & threonine . Alanine deamination via Transaminase directly yields pyruvate. alanine α -ketoglutarate pyruvate glutamate Aminotransferase (Transaminase) COO - CH 2 CH 2 C COO - O CH 3 HC COO - NH 3 + COO - CH 2 CH 2 HC COO - NH 3 + CH 3 C COO - O + +
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Serine is deaminated to pyruvate via Serine Dehydratase. Glycine , which is also product of threonine catabolism, is converted to serine by a reaction involving tetrahydrofolate (to be discussed later). HO CH 2 H C COO - NH 3 + C COO - O H 2 O NH 4 + C COO - NH 3 + H 2 C H 3 C H 2 O serine aminoacrylate pyruvate Serine Dehydratase
Background image of page 6
The 4-C Krebs Cycle intermediate oxaloacetate is produced from aspartate & asparagine . Aspartate transamination yields oxaloacetate . Aspartate is also converted to fumarate in Urea Cycle. Fumarate is converted to oxaloacetate in Krebs cycle. aspartate α -ketoglutarate oxaloacetate glutamate Aminotransferase (Transaminase) COO - CH 2 CH 2 C COO - O COO - CH 2 HC COO - NH 3 + COO - CH 2 CH 2 HC COO - NH 3 + COO - CH 2 C COO - O + +
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Asparagine loses the amino group from its R-group by hydrolysis catalyzed by Asparaginase . This yields aspartate, which can be converted to oxaloacetate, e.g., by transamination. C CH 2 HC COO - NH 3 + O H 2 N COO - CH 2 HC COO - NH 3 + H 2 O NH 4 + asparagine aspartate Asparaginase
Background image of page 8
The 4-C Krebs Cycle intermediate succinyl-CoA is produced from isoleucine, valine, & methionine. Propionyl-CoA , an intermediate on these pathways, is also a product of β -oxidation of fatty acids with an odd number of C atoms.
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
The branched chain amino acids initially share in part a common pathway.
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}