Asparagine aspartic acid system

It is noteworthy that there is another limiting factor in the choice of amino acid types at the junction sites which affect the enzymatic process of the intein. For example, in the case of SceVMA (also called PI-Seel) from the IMPACT system, proline, cysteine, asparagine, aspartic acid, and arginine cannot be at the C-terminus of the N-terminal target protein just before the intein sequence. The presence of these residues at this position would either slow down the N-S acyl shift dramatically or lead to immediate hydrolysis of the product from the N-S acyl shift [66]. The compatibility of amino acid types at the proximal sites depends on the specific inteins and needs to be carefully considered during the design of the required expression vectors. The specific amino acid requirements at a particular splicing site depends on the specific intein used and is thus a crucial point in this approach. 

The presence of asparaginase has also been reported in certain plant tissues (49, 50), but a recent study by Lees et al. (51), in which they used U-14C-asparagine to provide a sensitive assay system for asparagine conversion to aspartic acid, failed to show any asparaginase activity in extracts of wheat or lupin seedlings. 

Freeze-dried DOM samples collected with the siphon-elution system (Kuzyakov and Siniakina, 2001) for the first time showed diurnal dynamics in the molecular-chemical composition of maize rhizodeposits (Kuzyakov et al., 2003). In a forthcoming study with maize, Melnitchouck et al. (2005) showed that amino acids, especially aspartic acid, asparagine, glutamic acid, phenylalanine, leucine and isoleucine contributed to the more intensive rhizodeposition during daytime than during nighttime. Furthermore, the maximum of thermal volatilization of peptides at low pyrolysis temperature in Figure 14.8 indicates the rhizodeposition or microbial formation of free amino acids rather than amino acids bound in peptides or trapped in soil humic substances. 

It is clear that biological systems can manage the chemical reactivity of unstable species. For example, oxalo-acetate—a metabolic intermediate in terran metabolism that is a precursor of citric acid, malic acid, and the amino acid aspartic acid—decarboxylates readily, with a half-life measured in minutes at room temperature at neutral pH. The half-life for the decarboxylation of oxaloacetate drops to seconds at high temperatures in pure water. It is not clear how microorganisms that live at high temperatures manage the instability of oxaloacetate, which is a key intermediate in standard biochemistry for the formation of amino acids, such as aspartate, and asparagine. 

The earlier discussion on the effects of additives or impurities on crystal growth (Section 11.3.2) suggests that impurity incorporation is often surface specific. Black and Davey (1988) have reviewed much of the available information on the crystallization of amino acids. Amino acids are interesting model systems because of their common zwitterion group coupled with a variety of side chains, which may be present on a particular crystal face. L-asparagine can accommodate some 15% of L-aspartie acid as a mixed crystal (solid solution). From the effects of aspartic acid on the habit of asparagine crystals it is believed that aspartic acid primarily is incorporated at the 010 face whose growth rate is considerably reduced. 

Asparagine prebiotic systems, 871 Aspartate transcarbamylase zinc, 606 Aspartic acid metal complexes, 858 prebiotic systems, 871 Aspartic acid, p-carboxy-synthesis... 

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