Biochemistry of Amino Acids - A. Meister 1961

Natural Amino Acids
Other Natural Amino Acids
Sulfur-Containing Amino Acids

Class="center">L-Djenkolic Acid (Formaldehyde L-Cysteine thioacetal)

Djenkolic acid was first isolated from the urine of Java residents who consume djenkol beans (Pithecolobium lobatum) [231]. Although these beans are a popular food item, they exhibit a certain degree of toxicity. Djenkolic acid has also been isolated directly from the beans and obtained via chemical synthesis [231–233].

Felinine

This amino acid was first discovered during the chromatographic analysis of cat urine. Shortly thereafter, it was isolated, and its molecular Structure was tentatively determined [234]. The amount of felinine in feline urine is quite significant, with excretion rates sometimes reaching up to 120 mg per day. Felinine has been found exclusively in the urine of carnivorous species belonging to the felid family.

L-Cysteic Acid (β-sulfo-α-aminopropionic acid)

Cysteic acid is found in the outer layers of sheep wool [235]. The presence of this amino acid in a free state within urine and Tissues is attributed to its formation during cysteine oxidation (p. 380).

Taurine (2-aminoethanesulfonic acid)

Taurine occurs in a free state in various PLANT AND ANIMAL tissues [236, 237] and forms part of Bile in the form of taurocholic acid. Taurine is formed during cysteine METABOLISM (p. 384). Guanidotaurine has been detected in the Muscles of annelid worms [238]. Guanidotaurine and carbamyltaurine appear in rat urine following a taurine load [239].

This amino acid was initially obtained chemically from cysteine [240], and only recently has a similar enzymatic reaction been established (p. 380). Cysteine sulfinic acid and its decarboxylation product, hypotaurine HO₂SCH₂CH₂NH₂, have been found in a free state in the rat Brain [241].

Lanthionine [β,β'-thiodi(α-aminopropionic) acid]

The meso- and DL-forms of this amino acid have been isolated from alkaline wool hydrolysates and obtained synthetically [242–245]. Lanthionine is a component of the Antibiotics subtilin and nisin. These antibiotics also contain a methyl-substituted lanthionine, whose molecule is assigned the following structure [246, 247]:

Following the desulfurization of "methyllanthionine" by reduction with Raney nickel and subsequent Treatment with dinitrofluorobenzene, DNP-L-Alanine and DNP-D-α-aminobutyric acid were obtained. The configuration of the third asymmetric carbon atom in "methyllanthionine" remains unknown.

(+)-S-Methyl-L-cysteine sulfoxide

This amino acid has been isolated from cabbage [248] and turnips [249]. It is also found in other plants (radishes, broccoli, cauliflower). Its structure was established through chemical investigation of the natural product and comparison with the synthetic acid. Unlike Methionine, S-methylcysteine is not oxidized at room Temperature to the corresponding sulfoxide [249]. Consequently, The formation of the sulfoxide As a result of S-methylcysteine oxidation during plant material Processing is unlikely. S-methylcysteine sulfoxide partially accounts for the characteristic odor of certain vegetables (e.g., boiled cabbage).

(−)-S-Methyl-L-cysteine

S-Methyl-L-cysteine was relatively recently isolated from Phaseolus vulgaris. This amino acid likely serves as a precursor to the corresponding sulfoxide (see above), and it is possible that both Amino Acids are interconverted during metabolic processes [575].

Alliin [(+)-S-allyl-L-cysteine sulfoxide]

Alliin has been isolated from garlic bulbs. Its structure was established by comparing the isolated amino acid with one obtained via chemical synthesis. All 4 possible isomers of alliin have been obtained; the distinguishing feature of the natural isomer is that it contains an asymmetric sulfur atom. Upon the action of the enzyme alliinase, alliin is converted into allicin, which is responsible for the characteristic odor of garlic [250, 251] (p. 379).

α-Amino-S-dimethyl-γ-butyrothetin

This compound, which is a methylsulfonium derivative of methionine, has been found in cabbage, asparagus, and other vegetables [252, 253]. Apparently, other related compounds also occur in nature [254].

The other Sulfur-containing amino acids listed below have also been found in biological entities, but they have not been isolated preparatively from natural sources nor fully characterized.

L-Homocysteine (see p. 374)

L-Homocystine (see p. 374)

L-Cystathionine (see p. 367)

Cystine disulfoxide (see p. 383)

The betaine of ergothioneine, obtained from ergot, incorporates The amino acid thiolhistidine. Ergothioneine has been detected in erythrocytes [255]; thiolhistidine has not been found as a constituent of Proteins [256] (p. 394).