β-Hydroxy β-methylbutyryl-coenzyme A (HMB-CoA), also known as 3-hydroxyisovaleryl-CoA, is a metabolite of L-leucine that is produced in the human body. Its immediate precursors are β-hydroxy β-methylbutyric acid (HMB) and β-methylcrotonoyl-CoA (MC-CoA). It can be metabolized into HMB, MC-CoA, and HMG-CoA in humans.
3D model (JSmol)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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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Metabolic impairment diverts methylcrotonyl CoA to 3-hydroxyisovaleryl CoA in a reaction catalyzed by enoyl-CoA hydratase (22, 23). 3-Hydroxyisovaleryl CoA accumulation can inhibit cellular respiration either directly or via effects on the ratios of acyl CoA:free CoA if further metabolism and detoxification of 3-hydroxyisovaleryl CoA does not occur (22). The transfer to carnitine by 4 carnitine acyl-CoA transferases distributed in subcellular compartments likely serves as an important reservoir for acyl moieties (39–41). 3-Hydroxyisovaleryl CoA is likely detoxified by carnitine acetyltransferase producing 3HIA-carnitine, which is transported across the inner mitochondrial membrane (and hence effectively out of the mitochondria) via carnitine-acylcarnitine translocase (39). 3HIA-carnitine is thought to be either directly deacylated by a hydrolase to 3HIA or to undergo a second CoA exchange to again form 3-hydroxyisovaleryl CoA followed by release of 3HIA and free CoA by a thioesterase.
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