Ethionine is a non-proteinogenic amino acid structurally related to methionine, with an ethyl group in place of the methyl group.
Ethionine is an antimetabolite and methionine antagonist. It prevents amino acid incorporation into proteins and interferes with cellular use of adenosine triphosphate (ATP). Because of these pharmacological effects, ethionine is highly toxic and is a potent carcinogen.[1]
Djenkolic acid was first isolated by Van Veen and Hyman[6] from the urine of the natives of Java who had eaten the djenkol bean and were suffering from poisoning. They then succeeded in isolating the djenkolic acid crystals from the djenkol beans treated with Ba(OH)2 at 30°C for a prolonged period of time.[2]
Djenkolic acid was later reported to be found as much as 20 grams in every kilogram of dry djenkol beans, and it has also been reported to be found to a lesser extent in the seeds of other leguminous plants such as Leucaena esculenta (2.2 g/kg) and Pithecolobium ondulatum (2.8 g/kg).[3]
Du Vigneaud and Patterson managed to synthesize djenkolic acid by the condensation of methylene chloride with 2 moles of L-cysteine in liquid ammonia and to show that their synthetic compound was identical with the naturally occurring djenkolic acid.[2] Later on, Armstrong and du Vigneaud prepared djenkolic acid by the direct combination of 1 mole of formaldehyde with 2 moles of L-cysteine in a strongly acid solution.[7]
The toxicity of djenkolic acid in humans arises from its poor solubility under acidic conditions after consumption of the jenkol bean.[3] The amino acid precipitates into crystals which cause mechanical irritation of the renal tubules and urinary tract, resulting in symptoms such as abdominal discomfort, loin pains, severe colic, nausea, vomiting, dysurea, gross hematuria, and oliguria, occurring 2 to 6 hours after the beans were ingested.[4] Urine analysis of patients reveals erythrocytes, epithelial cells, protein, and the needle-like crystals of djenkolic acid. Urolithiasis can also happen, with djenkolic acid as the nucleus. In young children it has also been reported to produce painful swelling of the genitalia.[5]
Treatment for this toxicity requires hydration to increase urine flow and alkalinization of urine by sodium bicarbonate. Furthermore, this poisoning can be prevented when consuming djenkol beans by boiling them beforehand, since djenkolic acid is removed from the beans.[4]
Djenkolic acid (or sometimes jengkolic acid) is a sulfur-containing non-protein amino acid naturally found in djenkol beans of the South-East Asian legumes jengkol (Archidendron jiringa). This compound consists of two cysteine radicals connected by a methylene group between the sulfurs, or it is 2-amino-3-[(2-amino-3-hydroxy-3-oxopropyl)sulfanylmethylsulfanyl] propanoic acid. It is toxic to humans, especially causing nephrotoxicity.
Nutritional sources of cystine are virtually free of the toxic side effects associated with the single molecule of cysteine, N-acetyl cysteine. The greatest dietary source of cystine is bio-active, unpasteurized or low-heat pasteurized undenatured whey proteins.[citation needed]
Disulfide bonds can be broken at temperatures above about 150 °C, especially at low moisture levels (below about 20%)[3].
Supplemental N-acetyl cysteine is claimed to be a source of cystine, but the dose of this supplement is limited by side effects. One of the richest nutritional sources of cystine in the diet is undenatured whey proteins from milk. The disulfide-bonded cystine is not digested or significantly hydrolized by the stomach, but is transported by the blood stream to the tissues of the body. Here, within the cells of the body, the weak disulfide bond is cleaved to give cysteine, from which glutathione can be synthesized.
The disulfide link is readily reduced to give the corresponding thiol, cysteine. This reaction is typically effected with thiols such as mercaptoethanol or dithiothreitol.
(SCH2CH(NH2)CO2H)2 + 2 RSH ? 2 HSCH2CH(NH2)CO2H + RSSR
Cystine is the amino acid dimer formed when a pair of cysteine molecules are joined by a disulfide bond. It is described by the formula (SCH2CH(NH2)CO2H)2. It is a colorless solid, and melts at 247-249 °C. It was discovered in 1810 by William Hyde Wollaston but was not recognized as a component of proteins until it was isolated from the horn of a cow in 1899.[1] Through formation of disulfide bonds within and between protein molecules, cystine is a significant determinant of the tertiary structure of most proteins. Disulfide bonding, along with hydrogen bonding and hydrophobic interactions is partially responsible for the formation of the gluten matrix in bread. Human hair contains approximately 5% cystine by mass.[2]
Cysteine sulfinic acid is an intermediate in cysteine metabolism.
It is formed by cysteine dioxygenase.