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β-Hydroxybutyrate is the most abundant of the ketone bodies, followed by acetoacetate and finally acetone. [6] β-Hydroxybutyrate and acetoacetate can pass through membranes easily, and are therefore a source of energy for the brain, which cannot directly metabolize fatty acids.
Ketone bodies are transported from the liver to other tissues, where acetoacetate and β-hydroxybutyrate can be reconverted to acetyl-CoA to produce reducing equivalents (NADH and FADH 2), via the citric acid cycle. Though it is the source of ketone bodies, the liver cannot use them for energy because it lacks the enzyme thiophorase (β ...
β-Hydroxybutyric acid, also known as 3-hydroxybutyric acid or BHB, is an organic compound and a beta hydroxy acid with the chemical formula CH 3 CH(OH)CH 2 CO 2 H; its conjugate base is β-hydroxybutyrate, also known as 3-hydroxybutyrate. β-Hydroxybutyric acid is a chiral compound with two enantiomers: D-β-hydroxybutyric acid and L-β-hydroxybutyric acid.
β-Hydroxybutyrate, BHB, is also synthesized within liver cells; this is accomplished through the metabolism of fatty acids. Through a series of reactions, acetoacetate is first produced; and it is this acetoacetate that is reduced into β-hydroxybutyrate, catalyzed by the β-hydroxybutyrate dehydrogenase enzyme.
The test does not measure β-hydroxybutyrate, the most abundant ketone in the body; during treatment of ketoacidosis β-hydroxybutyrate is converted to acetoacetate so the test is not useful after treatment begins [11] and may be falsely low at diagnosis. [14] Similar tests are used in dairy cows to test for ketosis. [15]
Alternatively, acetoacetate can spontaneously degrade to a third ketone body (acetone) and carbon dioxide, which generates much greater concentrations of acetoacetate and D-β-hydroxybutyrate. The resulting ketone bodies cannot be used for energy by the liver so are exported from the liver to supply energy to the brain and peripheral tissues.
Two acetyl-CoA molecules condense to form acetoacetyl-CoA, which gives rise to the formation of acetoacetate and β-hydroxybutyrate. [16] Acetoacetate, β-hydroxybutyrate, and their spontaneous breakdown product acetone [ 18 ] are frequently, but confusingly, known as ketone bodies (as they are not "bodies" at all, but water-soluble chemical ...
Acetoacetate and D-β-hydroxybutyrate are exported to non-hepatic tissues, where they are converted back into acetyl-coA and used for fuel. Acetone and carbon dioxide on the other hand are exhaled, and not allowed to accumulate under normal conditions. Acetoacetate and D-β-hydroxybutyrate freely interconvert through the action of D-β ...