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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 ...
Both acetoacetate and beta-hydroxybutyrate are acidic, and, if levels of these ketone bodies are too high, the pH of the blood drops, resulting in ketoacidosis. Ketoacidosis is known to occur in untreated type I diabetes (see diabetic ketoacidosis ) and in alcoholics after prolonged binge-drinking without intake of sufficient carbohydrates (see ...
Beta-Hydroxybutyrate 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.
Although beta-hydroxybutyrate is the predominant circulating ketone, urine test strips only measure acetoacetate. Urinary ketones often correlate poorly with serum levels because of variability in excretion of ketones by the kidney, influence of hydration status, and renal function. [1] [8]
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 ...
As with tests for glucose, acetoacetate can be tested by a dipstick or by a lab. The results are reported as small, moderate, or large amounts of acetoacetate. A small amount of acetoacetate is a value under 20 mg/dL; a moderate amount is a value of 30–40 mg/dL, and a finding of 80 mg/dL or greater is reported as a large amount.
The encoded protein forms a homotetrameric lipid-requiring enzyme of the mitochondrial membrane and has a specific requirement for phosphatidylcholine for optimal enzymatic activity. The encoded protein catalyzes the interconversion of acetoacetate and (R)-3-hydroxybutyrate, the two major ketone bodies produced during fatty acid catabolism.
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]