Asparagine, deamination

Two amino acids—asparagine and glutamine—contain acid-amide groups in the side chains, from which NH3 can be released by hydrolysis (hydrolytic deamination). In the blood, glutamine is the most important transport molecule for amino nitrogen. Hydrolytic deamination of glutamine in the liver also supplies the urea cycle with NH3. 

L-Asparaginase [a SPAR a gi nase] catalyzes the deamination of asparagine to aspartic acid and ammonia. The form of the enzyme used chemotherapeutically is derived from bacteria. 

Deamination. Aspartic acid and asparagine undergo a slow, reversible deamination reaction. The aspartic acid deamination reaction, which produces fumaric acid and ammonia, can be written as... 

As mentioned in Section 1.1, the first diazotization of amines, followed by dediazoniation, was carried out by Piria in 1848, well before Griess discovered and isolated aromatic diazo compounds (1858). Piria added an impure HNO3 —HCl solution to a mixture of asparagine and aspartic acid in water and obtained malic acid (7-1). It was not possible for Piria, however, to realize that the primary reaction products were diazonium ions. Yet, Piria s process was one of the few types of reaction via aliphatic diazonium ions that became important for synthetic purposes, after Ingold s group (Brewster et al., 1950) discovered that a-amino acids undergo clean retentive deamination (see Sect. 7.7). 

S)-Malamide (5) is also hydrolyzed selectively to L-J -malamidic acid (16) using barium hydroxide as the base [11]. A more straightforward synthesis of 16 can be accomplished in one step by nitrous acid deamination of the inexpensive L-asparagine (15) [23,24]. 

Lloyd and Joy (1978) have confirmed the transmination of asparagine as a major pathway of the breakdown of the amide in leaves. The product 2-oxosuccinamate may be deaminated, but the majority was reduced to 2-hydroxysuccinamate which tended to accumulate. Very low levels of activity of the asparagine aminotransferase were detected in maturing pea seeds compared to the K+-activated asparaginase (K. W. Joy, personal communication). 

In contrast to the subunits that form the various types of LDH, those of aldolase are coded for by a single gene therefore, the conversion of a to jS is a posttranscriptional event involving the deamination of a single asparagine residue in the a-subunits. 

The liberated amino acids may be used for protein synthesis, or to provide energy by oxidation of the carbon skeleton after deamination. Ammonia produced in the latter reaction can be prevented from reaching toxic levels by fixation into glutamine and asparagine. 

Fig. 1.6. Formation of 3-aminopropionamide (3-APA) from the Strecker reaction of asparagine and subsequent deamination to acrylamide (according to Granvogl et al., 2006)...

Ammonia (NHj) is found in foods mainly as a product of free nucleotide deamination, such as deamination of adenosine 5 -monophosphate (AMP) to inosine 5 -monophosphate, and as a product of deamination of the amino acid amides asparagine and glutamine. In acidic foods, ammonia is present almost exclusively in the form of ammonium salts. 

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