Dhurrin is a

cyanogenic Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of a ...

glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...

produced in many

plants Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

. Discovered in multiple

sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...

varieties in 1906 as the culprit of cattle poisoning by

hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on an ...

, dhurrin is most typically associated with ''

Sorghum bicolor ''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a Poaceae, grass species cultivated for its grain, which is used for food for humans, animal feed, and ethan ...

'', the organism used for mapping the

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

of dhurrin from

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...

. Dhurrin's name is derived from the

Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...

word for sorghum, transliterated to "Dhura."

Biosynthesis

Regulation in ''Sorghum bicolor''

In ''Sorghum bicolor'', dhurrin production is regulated at the transcriptional level and varies depending on the plant’s age and available nutrients. Dhurrin content within ''S. bicolor'' can be correlated to the amount of

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...

and

translated Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

CYP79A1 and CYP71E1, two

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...

bound members of the

cytochrome P450 Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

. While transcription and translation of these two enzymes is relatively higher for the first few days of growth, transcription is greatly reduced past one week of growth. After five weeks of growth, transcription and translation of both enzymes in the leaves becomes undetectable, while stems in said plants maintain the minimal production of both enzymes. With the addition of excess

nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...

, transcription of both enzymes increases, though not to the levels seen in early development. The last enzyme in dhurrin synthesis, UGT85B1, is a soluble enzyme which exchanges glucose from

UDP-glucose Uridine diphosphate glucose (uracil-diphosphate glucose, UDP-glucose) is a nucleotide sugar. It is involved in glycosyltransferase reactions in metabolism. Functions UDP-glucose is used in nucleotide sugar metabolism as an activated form of gl ...

to the

aglycone An aglycone (aglycon or genin) is the compound remaining after the glycosyl group on a glycoside is replaced by a hydrogen atom. For example, the aglycone of a cardiac glycoside would be a steroid molecule. Detection A way to identify aglycone ...

of dhurrin and forms the

glycosidic bond A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group ...

Transgenic synthesis

Addition of both CYP79A1 and CYP71E1 into the genomes of ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter a ...

'' and ''

Nicotiana tabacum ''Nicotiana tabacum'', or cultivated tobacco, is an annually grown herbaceous plant of the ''Nicotiana'' genus. The plant is tropical in origin, is commonly grown throughout the world, and is often found in cultivation. It grows to heights bet ...

'' has been shown to be sufficient for Dhurrin production to occur. Both of these enzymes are sufficient and necessary for Dhurrin production, as removal of the CYP79A1

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

from the ''Sorghum bicolor'' genome results in plants lacking dhurrin content. This strain could theoretically be used as a safer crop for

fodder Fodder (), also called provender (), is any agriculture, agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, domestic rabbit, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food g ...

in arid environments where sorghum is the only available grain. ''In vitro'' biosynthesis of dhurrin has been constructed in both

microsomes In cell biology, microsomes are heterogeneous vesicle-like artifacts (~20-200 nm diameter) re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; microsomes are not present in healthy, liv ...

recovered from ''Sorghum bicolor''

seedlings A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...

and in

micelles A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloid, colloidal suspension (also known as associat ...

Toxicity

Mammals

Mammalian intestines contain multiple

glucosidases Glucosidases are the glycoside hydrolase enzymes categorized under the EC number 3.2.1. Function Alpha-glucosidases are enzymes involved in breaking down complex carbohydrates such as starch and glycogen into their monomers. They catalyze ...

which efficiently

hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

glycosidic bonds. Upon hydrolysis of the glycosidic bond, the aglycone of dhurrin rapidly degrades to form hydrogen cyanide which is then absorbed into the bloodstream. Lethal dosage of dhurrin in humans and other mammals is theoretically high as one molecule of hydrogen cyanide is produced per molecule of dhurrin. Content of dhurrin by mass in sorghum is relatively low with respect to overall plant matter. As such, it would require a human to eat a considerably large amount of raw sorghum before experiencing adverse effects. In arid environments, sorghum is the best option for cereal grain and fodder as it can withstand extreme drought conditions. Animals consuming the raw sorghum as fodder are much more likely to eat an amount that would contain a lethal dosage of dhurrin for their respective species and can result in animal loss due to hydrogen cyanide poisoning.

As an insect repellent

In response to external damage to the stem, sorghum varieties can release dhurrin at the damage site. This response has been shown to repel insects as

transgenic A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...

sorghum made unable to produce dhurrin was heavily favored by herbivorous insects when compared to

wild-type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, "m ...

sorghum varieties.{{cite journal, last1=Krothapalli, first1=Kartikeya, title=Forward Genetics by Genome Sequencing Reveals That Rapid Cyanide Release Deters Insect Herbivory of Sorghum Bicolor, journal=Genetics, date=October 2013, volume=195, pages=309–318, url=http://www.genetics.org/content/195/2/309.full.pdf+html?sid=39121ec4-c3f7-43f8-a7d0-8e5107d03b40, doi=10.1534/genetics.113.149567, pmid=23893483, pmc=3781961

References

Cyanogenic glycosides Phenols Glucosides