Isoaspartate

M. V. Paranandi, A. W. Guzzetta, W. S. Hancock, D. W. Aswad, Deamidation and Isoaspartate Formation During in vitro Aging of Recombinant Tissue Plasminogen Activator , J. Biol. Chem. 1994, 269, 243-253. 

Aswad D.W., Parandandi M.W., and Schurter B.T. (2000), Isoaspartate in peptides and proteins formation, significance and analysis, J. Pharm. Biomed. Anal. 21, 1129-1136. 

Whether there is any other connection between anticonvulsant activity and camosine s antiaging actions is obviously highly speculative. It may be relevant to note that epileptic seizures and a shortened life span, together with altered protein accumulation, are consequences of PIMT-deficiency in mice, while treatment with valproic acid, an anticonvulsant, partially suppresses these symptoms including effects on life span (Yamamoto et ah, 1998). Conversely, PIMT overexpression can increase life span of Drosophila (Bennet et ah, 2003). Furthermore, the chemistry of some anticonvulsants (ethosuximide) resembles quite closely the structure of the succinimide intermediate formed during both asparagine deamidation and PIMT-mediated repair of isoaspartate residues. One conjectures whether there are any relationships between these... 

The biological role of PIMT involves the selective methylation of isoaspartate residues followed by a demethylation step to reform the succi-nimide intermediate. The demethylation causes the release of methanol which can be converted to formaldehyde and finally to formic acid, as demonstrated in rat brain preparations. It was found that S-adenosyl-methionine (SAM), the methyl donor, caused formaldehyde levels to rise in the rat brain homogenates, thus suggesting that excessive formaldehyde may be a precipitating factor in Parkinsons s disease (PD) (Lee et ah, 2008). It is possible that carnosine could suppress formaldehyde toxicity by reacting with it to generate a carnosine-formaldehyde adduct. This should be a relatively easy experiment to perform to test this prediction. 

In general, transition metal ions are undesired in protein formulations because they can catalyze physical and chemical degradation reactions in proteins. However, specific metal ions are included in formulations when they are cofactors to proteins and in suspension formulations of proteins where they form coordination complexes (e.g., zinc suspension of insulin). Recently, the use of magnesium ions (10-120 mM) has been proposed to inhibit the isomerization of aspartic acid to isoaspartic acid (63). 

Aswad, D. W., ed. (1995) Deamidation and Isoaspartate Formation in Peptides and Proteins, CRC Press, Boca Raton, Florida... 

Shimizu T., Matsuoka Y., and Shirasawa T. (2005). Biological significance of isoaspartate and its repair system. Biol. Pharm. Bull. 28 1590-1596. 

Johnson BA, Shirokawa J, Hancock W, Spellman M, Basa L, Aswad D. Formation of isoaspartate at two distinct sites during in vitro aging of human growth hormone. J Biol Chem 1989 264 14262-14271. 

Isoaspartate versus Aspartate Product Ratios of RG2 Antibodies0... 

DEAMIDATION AND ISOASPARTATE FORMATION DURING in Vitro AGING OF A RECOMBINANT HEPATITIS E VACCINE CANDIDATE... 

Deamidation and Isoaspartate Formation in Hepatitis E Vaccine III. Results and Discussion... 

A. Kinetics of Isoaspartate Formation During In Vitro Aging... 

To determine if r62-kDa accumulates isoaspartate during in vitro aging under mild conditions, a sample of the purified protein was incubated at 30°C for 5 days in a pH 7.5 Tris buffer. 

B. Isoaspartate Containing Tryptic Peptides of Aged Recombinant 62-kDa... 

Samples of control and aged r62-kDa were reduced, alkylated, and then digested with trypsin as described in the text. Each digest was split into two portions. One portion was subjected to reverse phased HPLC at low pH with uV detection to generate a peptide elution profile (left panels). The second portion was enzymatically methylated with [methyl- H] Adomet to radiolabel all of the isoaspartate bearing peptides. The labeled peptides were then chromatographed under the same conditions as the first portion (right panels) and detected by radioactivity. 

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