Stickland fermentation or The Stickland Reaction is the name for a chemical reaction that involves the coupled

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

and reduction of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s to organic acids. The

electron donor In chemistry, an electron donor is a chemical entity that transfers electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. An obsolete definition equated an electron dono ...

amino acid is oxidised to a volatile

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

one carbon atom shorter than the original amino acid. For example,

alanine Alanine (symbol Ala or A), or α-alanine, is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group sid ...

with a three carbon chain is converted to

acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...

with two carbons. The electron acceptor amino acid is reduced to a volatile carboxylic acid the same length as the original amino acid. For example,

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

with two carbons is converted to acetate. In this way, amino acid fermenting microbes can avoid using hydrogen ions as electron acceptors to produce hydrogen gas. Amino acids can be Stickland acceptors, Stickland donors, or act as both donor and acceptor. Only

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...

cannot be fermented by Stickland reactions, and is oxidised. With a typical amino acid mix, there is a 10% shortfall in Stickland acceptors, which results in

hydrogen production Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Article in press. Most hydrogen is ''gray hydrogen'' made through steam methane reforming. In this process, ...

. Under very low hydrogen partial pressures, increased uncoupled anaerobic oxidation has also been observed. It occurs in proteolytic clostridia such as: '' C. perfringens'', '' Clostridioides difficile'', '' C. sporogenes'', and '' C. botulinum''. Additionally,

sarcosine Sarcosine, also known as ''N''-methylglycine, or monomethylglycine, is a amino acid with the formula CH3N(H)CH2CO2H. It exists at neutral pH as the zwitterion CH3N+(H)2CH2CO2−, which can be obtained as a white, water-soluble powder. Like some ...

and betaine can act as electron acceptors.

References

Biochemical reactions Name reactions {{Biochem-stub