Aspartic acid from proteins

Historically, L-aspartic acid was produced by hydrolysis of asparagine, isolated from protein hydrolysates, or by the resolution of chemically synthesized d,l-aspartate. With the discovery of aspartase (L-aspartatc ammonia lyase. Enzyme Commission [EC] 4.3.1.1) [5] fermentation routes to L-aspartic acid quickly superseded the initial chemical methods. After further characterization, enzymatic routes to the production aspartic acid from ammonium fumarate using aspartase 317... 

L-Aspartic acid has been isolated in relatively small quantities from numerous proteins by methods which have been employed primarily for analytical purposes. The isolation of aspartic acid as barium-DL-aspar-tate, first described by Fischer (280) in 1901, has been applied to different proteins by Fischer, Abderhalden, Osborne, Jones and other workers as recently as 1928 (488) even though, in 1910, Osborne and Jones (616) were able to recover only 42% of aspartic acid from a mixture of pure amino acids. By Foreman s (318) modification of the Rittbausen (669, 670) procedure, calcium aspartate and glutamate are precipitated with calcium hydroxide and ethanol, calcium is removed from the precipitate as the oxalate and aspartic acid is isolated as the copper salt. Jones et al. (419,420, 431, 433-435), Bergmann and Niemann (89, 90), and Chibnall et al. (151) have isolated aspartic acid from various proteins by this method. Other investigators have employed for this purpose various combinations of barium, lead and copper aspartates. 

Fig. 3. The pH dependence, where A, B, and C represent regions corresponding to the p-K s of glutamic and aspartic acids, lysine, and argenine, respectively, of (a) protein swelling, and (b) protein acid-binding capacity. Adapted from Ref. 3.

Figure 1.9 Examples of functionally important intrinsic metal atoms in proteins, (a) The di-iron center of the enzyme ribonucleotide reductase. Two iron atoms form a redox center that produces a free radical in a nearby tyrosine side chain. The iron atoms are bridged by a glutamic acid residue and a negatively charged oxygen atom called a p-oxo bridge. The coordination of the iron atoms is completed by histidine, aspartic acid, and glutamic acid side chains as well as water molecules, (b) The catalytically active zinc atom in the enzyme alcohol dehydrogenase. The zinc atom is coordinated to the protein by one histidine and two cysteine side chains. During catalysis zinc binds an alcohol molecule in a suitable position for hydride transfer to the coenzyme moiety, a nicotinamide, [(a) Adapted from P. Nordlund et al., Nature 345 593-598, 1990.)...

The importance of Heinrich Ritthausen s fundamental studies, 1862 to 1899, on analytical procedures for the determination of amino acids in proteins has been emphasized in the biographical sketches which have been presented by Osborne (210), Vickery (289), and Chibnall (47). It is of particular interest to note here the prediction made by Ritt-hausen about 1870 that the amino acid composition would prove to be the most adequate basis for the characterization of proteins. Ritthausen and Kreusler (230) were the first, in 1871, to determine amino acids derived from proteins, and some of the values which they found for aspartic and glutamic acids are given in Table III (cited by Chibnall, 47, and Vickery, 286). 

Protein mixtures were well resolved on poly(aspartic acid)-silica columns using 0.05 mol/1 phosphate buffer, pH 6.0 and a gradient of sodium chloride from 0 to 0.6 mol/1. The columns displayed a high capacity and selectivity. Figure 3 shows the separation of several standard proteins with isoelectric points ranging from 4.7 to over 11. Peaks are sharp and show minimal tailing. The poly(aspartic acid) coating was quite stable the columns lasted for hundreds of hours of use without decrease in efficiency and capacity. 

Grb-2 facilitates the transduction of an extracellular stimulus to an intracellular signaling pathway, (b) The adaptor protein PSD-95 associates through one of its three PDZ domains with the N-methyl-D-aspartic acid (NMDA) receptor. Another PDZ domain associates with a PDZ domain from neuronal nitric oxide synthase (nNOS). Through its interaction with PSD-95, nNOS is localized to the NMDA receptor. Stimulation by glutamate induces an influx of calcium, which activates nNOS, resulting in the production of nitric oxide. 

Two amino acids—cysteine and tyrosine—can be synthesized in the body, but only from essential amino acid ptecutsots (cysteine from methionine and tyrosine from phenylalanine). The dietary intakes of cysteine and tytosine thus affect the requirements for methionine and phenylalanine. The remaining 11 amino acids in proteins are considered to be nonessential or dispensable, since they can be synthesized as long as there is enough total protein in the diet—ie, if one of these amino acids is omitted from the diet, nitrogen balance can stiU be maintained. Howevet, only three amino acids—alanine, aspartate, and glutamate—can be considered to be truly dispensable they ate synthesized from common metabolic intetmediates (pyruvate, ox-... 

The enormous diversity of protein stmcture and function comes from the many ways in which 20 amino acids can combine into polypeptide chains. Consider how many tetrapeptide chains can be made using Just two amino acids, cysteine and aspartic acid ... 

L and the D/L ratio approaches zero. After the death of the living organism, proteins start to spontaneously break down. An inter-conversion of the amino acids occurs from one chiral form (L) to a mixture of D- and L- forms following protein degradation this process is called amino acid racemisation. The extent of racemisation is measured by the ratio of D/L isomers and increases as a function of time and temperature. The longer the racemisation process continues the closer to 1 the ratio between the D- and L-forms becomes. If the D/L ratio is <1 it may be possible to use it to estimate age. The D/L ratio of aspartic acid and isoleucine are the most widely used for this dating technique [104]. Dates have been obtained as old as 200 000 years. However, it has been used mainly to date samples in the 5000 100 000 year range. Recent studies [ 105] mention an estimation of the method accuracy to be around 20%. 

---