Template talk:Leucine metabolism in humans

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Annotating the mevalonate pathway and usage in 3 articles

Latest comment: 6 years ago2 comments1 person in discussion

Leucine metabolism in humans

L-Leucine

Branched-chain amino
acid aminotransferase

Muscle: α-Ketoisocaproate (α-KIC)

Liver: α-Ketoisocaproate (α-KIC)

Branched-chain α-ketoacid
dehydrogenase (mitochondria)

KIC-dioxygenase
(cytosol)

Isovaleryl-CoA

β-Hydroxy
β-methylbutyrate
(HMB)

Excreted
in urine
(10–40%)

HMB-CoA

β-Hydroxy β-methylglutaryl-CoA
(HMG-CoA)

β-Methylcrotonyl-CoA
(MC-CoA)

β-Methylglutaconyl-CoA
(MG-CoA)

CO₂

O₂

CO₂

H₂O

CO₂

H₂O

(liver)
HMG-CoA
lyase

Enoyl-CoA hydratase

Isovaleryl-CoA
dehydrogenase

β-Hydroxybutyrate
dehydrogenase

Unknown
enzyme

Human metabolic pathway for HMB and isovaleryl-CoA relative to L-leucine.^[1]^[2]^[3] Of the two major pathways, L-leucine is mostly metabolized into isovaleryl-CoA, while only about 5% is metabolized into HMB.^[1]^[2]^[3]

@Boghog: This diagram currently suggests that mevalonate is metabolized directly into cholesterol, which it isn't; do you think it would help to clarify this if I added a "mevalonate pathway" annotation next to the line connecting mevalonate to cholesterol? If I were to add that annotation, I could use either an unpiped link to the article on the mevalonate pathway or a piped link to File:Mevalonate pathway.svg, which I think would be a better link target than the article for this purpose.

Also, β-hydroxybutyrate, acetoacetate, and β-hydroxybutyrate dehydrogenase all lack a metabolic pathway diagram at the moment. I realize that HMG-CoA (KEGG link) and acetoacetate (KEGG link) are generated through several metabolic pathways – not just from leucine – so I could indicate this in the caption if this diagram is transcluded to those articles. Alternatively, I could crop out everything above HMG-CoA or HMB-CoA in this diagram and add that to those articles instead. Besides this template, the only other high-quality image I've seen which illustrates those 3 articles I mentioned in a metabolic pathway is File:Ketogenesis.svg. Which of these diagrams do you think is better suited for those articles? Seppi333 (Insert 2¢) 07:36, 31 January 2018 (UTC)Reply

Nevermind, I went ahead and added the mevalonate pathway image file annotation and annotated the thiolase enzyme for acetyl-CoA↔acetoacetyl-CoA. Seppi333 (Insert 2¢) 15:17, 1 February 2018 (UTC)Reply

Section reflist

^ ^a ^b Wilson JM, Fitschen PJ, Campbell B, Wilson GJ, Zanchi N, Taylor L, Wilborn C, Kalman DS, Stout JR, Hoffman JR, Ziegenfuss TN, Lopez HL, Kreider RB, Smith-Ryan AE, Antonio J (February 2013). "International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB)". Journal of the International Society of Sports Nutrition. 10 (1): 6. doi:10.1186/1550-2783-10-6. PMC 3568064. PMID 23374455.
^ ^a ^b Zanchi NE, Gerlinger-Romero F, Guimarães-Ferreira L, de Siqueira Filho MA, Felitti V, Lira FS, Seelaender M, Lancha AH (April 2011). "HMB supplementation: clinical and athletic performance-related effects and mechanisms of action". Amino Acids. 40 (4): 1015–1025. doi:10.1007/s00726-010-0678-0. PMID 20607321. S2CID 11120110. HMB is a metabolite of the amino acid leucine (Van Koverin and Nissen 1992), an essential amino acid. The first step in HMB metabolism is the reversible transamination of leucine to [α-KIC] that occurs mainly extrahepatically (Block and Buse 1990). Following this enzymatic reaction, [α-KIC] may follow one of two pathways. In the first, HMB is produced from [α-KIC] by the cytosolic enzyme KIC dioxygenase (Sabourin and Bieber 1983). The cytosolic dioxygenase has been characterized extensively and differs from the mitochondrial form in that the dioxygenase enzyme is a cytosolic enzyme, whereas the dehydrogenase enzyme is found exclusively in the mitochondrion (Sabourin and Bieber 1981, 1983). Importantly, this route of HMB formation is direct and completely dependent of liver KIC dioxygenase. Following this pathway, HMB in the cytosol is first converted to cytosolic β-hydroxy-β-methylglutaryl-CoA (HMG-CoA), which can then be directed for cholesterol synthesis (Rudney 1957) (Fig. 1). In fact, numerous biochemical studies have shown that HMB is a precursor of cholesterol (Zabin and Bloch 1951; Nissen et al. 2000).
^ ^a ^b Kohlmeier M (May 2015). "Leucine". Nutrient Metabolism: Structures, Functions, and Genes (2nd ed.). Academic Press. pp. 385–388. ISBN 978-0-12-387784-0. Retrieved 6 June 2016. Energy fuel: Eventually, most Leu is broken down, providing about 6.0kcal/g. About 60% of ingested Leu is oxidized within a few hours ... Ketogenesis: A significant proportion (40% of an ingested dose) is converted into acetyl-CoA and thereby contributes to the synthesis of ketones, steroids, fatty acids, and other compounds
Figure 8.57: Metabolism of L-leucine

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[ISSN_position_stand_2013-1] Wilson JM, Fitschen PJ, Campbell B, Wilson GJ, Zanchi N, Taylor L, Wilborn C, Kalman DS, Stout JR, Hoffman JR, Ziegenfuss TN, Lopez HL, Kreider RB, Smith-Ryan AE, Antonio J (February 2013). "International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB)". Journal of the International Society of Sports Nutrition. 10 (1): 6. doi:10.1186/1550-2783-10-6. PMC 3568064. PMID 23374455.

[HMB_athletic_performance-related_effects_2011_reviewb-2] Zanchi NE, Gerlinger-Romero F, Guimarães-Ferreira L, de Siqueira Filho MA, Felitti V, Lira FS, Seelaender M, Lancha AH (April 2011). "HMB supplementation: clinical and athletic performance-related effects and mechanisms of action". Amino Acids. 40 (4): 1015–1025. doi:10.1007/s00726-010-0678-0. PMID 20607321. S2CID 11120110. HMB is a metabolite of the amino acid leucine (Van Koverin and Nissen 1992), an essential amino acid. The first step in HMB metabolism is the reversible transamination of leucine to [α-KIC] that occurs mainly extrahepatically (Block and Buse 1990). Following this enzymatic reaction, [α-KIC] may follow one of two pathways. In the first, HMB is produced from [α-KIC] by the cytosolic enzyme KIC dioxygenase (Sabourin and Bieber 1983). The cytosolic dioxygenase has been characterized extensively and differs from the mitochondrial form in that the dioxygenase enzyme is a cytosolic enzyme, whereas the dehydrogenase enzyme is found exclusively in the mitochondrion (Sabourin and Bieber 1981, 1983). Importantly, this route of HMB formation is direct and completely dependent of liver KIC dioxygenase. Following this pathway, HMB in the cytosol is first converted to cytosolic β-hydroxy-β-methylglutaryl-CoA (HMG-CoA), which can then be directed for cholesterol synthesis (Rudney 1957) (Fig. 1). In fact, numerous biochemical studies have shown that HMB is a precursor of cholesterol (Zabin and Bloch 1951; Nissen et al. 2000).

[Leucine_metabolism-3] Kohlmeier M (May 2015). "Leucine". Nutrient Metabolism: Structures, Functions, and Genes (2nd ed.). Academic Press. pp. 385–388. ISBN 978-0-12-387784-0. Retrieved 6 June 2016. Energy fuel: Eventually, most Leu is broken down, providing about 6.0kcal/g. About 60% of ingested Leu is oxidized within a few hours ... Ketogenesis: A significant proportion (40% of an ingested dose) is converted into acetyl-CoA and thereby contributes to the synthesis of ketones, steroids, fatty acids, and other compounds
Figure 8.57: Metabolism of L-leucine

[1]

[2]

[3]