3-Hydroxyisovaleric Acid (3-HIA) is formed from the metabolism of the branched-chain amino acid leucine. Methylcrotonyl-CoA carboxylase catalyzes an essential step in this pathway and is biotin dependent. Reduced activity of this enzyme leads to an alternate pathway of metabolism resulting in 3-hydroxyisovaleric acid.

3-Hydroxyisovaleric Acid (3-HIA) is formed from the metabolism of the branched-chain amino acid leucine. Methylcrotonyl-CoA carboxylase catalyzes an essential step in this pathway and is biotin dependent. Reduced activity of this enzyme leads to an alternate pathway of metabolism resulting in 3-hydroxyisovaleric acid.

Production of 3-hydroxyisovaleric acid begins with the conversion of 3-methylcrotonyl-CoA into 3-methylglutaconyl-CoA in the mitochondria by the biotin-dependent enzyme methylcrotonyl-CoA carboxylase.

3-Hydroxykynurenine is a metabolic intermediate of the kynurenine pathway that elicits neurotoxic effects.

3-Hydroxyphenylacetic acid and 4-hydroxyphenylacetic acid are produced by the bacterial fermentation of amino acids, much like Indoleacetic acid (IAA).

3-Hydroxyphenylacetic acid is a rutin metabolite and an antioxidant.

3-Hydroxypropionic acid (3-HPA) is a major urinary metabolite of propionic acid. Propionic acid is derived from dietary branched-chain amino acids, odd-chain fatty acids, and can be produced in the gut by bacterial fermentation of fiber. The biotindependent enzyme propionyl CoA carboxylase is responsible for metabolizing propionic acid to methylmalonyl CoA, which is subsequently isomerized to succinyl CoA. Decreased activity of this enzyme shunts propionyl CoA into alternative pathways which form 3-HPA.

Metabolite of propionic acid, precursor of methylmalonic acid via both biotin and Mg.

3-Hydroxypropionic Acid (3-HPA) is a major urinary metabolite of propionic acid. Propionic acid is derived from dietary branched-chain amino acids, oddchain fatty acids, and can be produced in the gut by bacterial fermentation of fiber. The biotin-dependent enzyme propionyl CoA carboxylase is responsible for metabolizing propionic acid to methylmalonyl CoA, which is subsequently isomerized to succinyl CoA. Decreased activity of this enzyme shunts propionyl CoA into alternative pathways which form 3-HPA.

3-HPMA is the main urinary metabolite of acrolein. Acrolein is an environmental pollutant, commonly used as an herbicide and in many different chemical industries. Acrolein is also present in the burning of cigarettes, gasoline, and oil. Certain bacteria produce acrolein, such as Clostridium. Acrolein metabolites are associated with diabetes and insulin resistance.

3-Hydroxyvaleric acid may be products of the condensation of propionyl-CoA with acetyl-CoA catalyzed by 3-oxoacyl-CoA thiolases. An increase amount of 3-hydroxyvaleric acid can be found in methylmalonic acidemia and propionic acidemia. 

Indoleacetic acid (IAA), or indole-3-acetate, is produced by the bacterial fermentation of the amino acid tryptophan.

IAA can be formed from several common gut microbes such as Clostridia species, Escherichia coli, and Saccharomyces species.

3-Indoleacetic is a Tryptophan byproduct of Clostria: C. stricklandii, C. litusburense, C. subterminale, and C. putrefaciens.

3-Indoleacetic is a Tryptophan byproduct of Clostria: C. stricklandii, C. litusburense, C. subterminale, and C. putrefaciens.

Both 1-methylhistidine and 3-methylhistidine are histidine metabolites which have been proposed as markers of meat intake. Note that some confusion exists in the literature regarding the numbering of atoms in the imidazole ring of histidine – 1 versus 3 – and thus, there is caution with interpretation and clinical significance of these two markers.

3-methylhistidine is a constituent of actin and myosin, the contractile proteins of skeletal muscles. Urinary excretion of 3-methylhistidine may be a result of muscle breakdown or consumption of meat fibers. Unlike 1-methylhistidine, 3-methylhistidine has been shown to increase in fasting states indicating catabolism of muscle tissue. Therefore, this marker is more variable with regards to animal protein consumption.