Glucose deamination

The amino acids are required for protein synthesis. Some must be supplied in the diet (the essential amino acids) since they cannot be synthesized in the body. The remainder are nonessential amino acids that are supplied in the diet but can be formed from metabolic intermediates by transamination, using the amino nitrogen from other amino acids. After deamination, amino nitrogen is excreted as urea, and the carbon skeletons that remain after transamination (1) are oxidized to CO2 via the citric acid cycle, (2) form glucose (gluconeogenesis), or (3) form ketone bodies. 

These points have important functional implications. While neuronal glutamate may come from glucose via pyruvate, the Krebs cycle and transamination of alpha-oxoglutamate, it seems likely that most of the transmitter originates from the deamination of glutamine. After release, the high-affinity uptake sites (transporters)... 

More-specific methods are available for identifying and quantitating the typical, amino sugar component of heparin (and some heparan sulfate species), namely, 2-deoxy-2-sulfoamino-D-glucose. Most of these methods are based on conversion of these residues into 2,5-anhydro-D-mannose by deamination with nitrous acid (see Section VIII,2). The 2,5-anhydro-D-mannose residues may be determined either colorimetrically,52-54 or fluorimetrically.55... 

Scheme 2. — Nitrous Acid Deamination of 2-Amino-2-deoxy-D-glucose and Its Glycosides.

In analogy with the deamination of aminocyclohexanes,17-21 it has been found that the deamination, with nitrous acid, of 2-amino-2-deoxyaldohexoses in which the amino group has an equatorial orientation leads to 2,5-anhydrohexoses, as exemplified by the deamination of 2-amino-2-deoxy-D-glucose (10) to 2,5-anhydro-D-mannose22-25 (11). 

In contrast to other 2,5-anhydroaldoses (which exhibit mutarota-tion, possibly due to the formation of hemiacetals28), 2,5-anhydro-D-glucose does not show any mutarotation.27 The importance of this compound as a potentially useful precursor to C-nucleosides warrants a reinvestigation of the deamination reaction, and the definitive proof of the structure of the compound. The readily accessible 2,5-anhydro-D-mannose (11) does not possess the cis-disposed side-chains at C-2 and C-5 that would be required of a synthetic precursor to the naturally occurring C-nucleosides, with the exception of a-pyrazomycin (8). The possibility of an inversion of the orientation of the aldehyde group in 11 by equilibration under basic conditions could be considered. 

Following their deamination, several amino acids can be converted into oxaloacetate via pyruvate or other components of the TCA cycle these are termed glucogenic amino acids because their carbon atoms may eventually appear in glucose (see Table 6.7). The carbon skeletons of other amino acids may be converted into acetyl-CoA or acetoacetyl-CoA and these are ketogenic amino acids. A few amino acids be metabolized through both glucogenic and ketogenic pathways. 

Glycogenolysis and glycogen synthesis P-oxidation of fatty acids transamination and deamination of amino acids Cori cycle and glucose-alanine cycle, which recycles substrates between muscle and liver. 

The nitrous acid deamination of 2-amino-2-deoxy-D-mannose (8), in the favored conformation, the amino group ofwhich is axially attached, leads, in contrast, uniquely to D-glucose,15 characterized, after oxidation by nitric acid, as D-glucaric acid (9). This result has also been verified by direct crystallization of the D-glucose and by assay with D-glucose oxidase.44"... 

Levene15 reported that heating of 2-amino-2-deoxy-D-mannose (8) in the presence of silver oxide leads to a crystalline, nitrogen-free compound to which he attributed the structure of 2,5-anhydro-D-glucose on the basis of its elemental analysis. The possibility of interconversion between the two chair forms Cl (d) — 1C (d), which would bring the amino group at C-2 into equatorial orientation, has been postulated.22 Without excluding this possibility, it remains to be proved that the deamination by silver oxide does, indeed, proceed by... 

In attempting to obtain 2,5-anhydro-D-glucose diethyl dithioacetal, Defaye58 performed the nitrous acid deamination of 2-amino-2-deoxy-D-glucose diethyl dithioacetal (27) under weakly acidic conditions (acetic acid and sodium nitrite), and obtained a principal product later shown59 to be ethyl 2-S-ethyl-l,2-dithio-a-D-mannofuranoside (28). Shortly before, Horton and coworkers60 had reported the forma-... 

This reaction has been compared81 with the nitrous acid deamination of 2-amino-2-deoxy-D-glucose attack by a bromonium ion could lead to an intermediate, alkyl-iodonium cation (2-C-I-Br) , which would decompose through nucleophilic attack by 0-5, which is antiparallel to the leaving group at C-2. 

Solvent can have a marked effect on deamination in other respects. For example, it is commonly found that the extent of rearrangement is greater, the more polar the solvent 29,44 45 this effect is attributed to the increased lifetime of carbonium-ion species and their rearrangement to species that are more thermodynamically stable. Reactions performed at different pH values may also give different products, as illustrated by the deamination of 2-amino-2-deoxy-D-glucose diethyl dithioacetal hydrochloride in solution in (a) aqueous acetic acid and (b) hydrochloric acid (see p. 65). 

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