Deamidated, isomerized, and racemized aspartyl and asparaginyl residues represent a significant part of the spontaneous damage to proteins that results from the aging process. The accumulation of these altered residues can lead to the loss of protein function and the consequent loss of cellular function. However, almost all cells in nature contain a methyltransferase that can recognize the major damaged form of the L-isoaspartyl residue, and some of these enzymes can also recognize the racemized D-aspartyl residue. The methyl esterification reaction can initiate the conversion of these altered residues to the normal L-aspartyl form, although there is no evidence yet that the L-asparaginyl form can be regenerated. This enzyme, the protein L-isoaspartate (D-aspartate) O-methyltransferase (EC 2.1.1.77), thus functions as a protein repair enzyme. The importance of this enzyme in attenuating age-related protein damage can be seen by the phenotypes of organisms where the gene encoding has been disrupted, or where its expression has been augmented.

中文翻译：

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化学和生化过程之间的衰老：蛋白质甲基化和对年龄受损的蛋白质的修复识别。

脱酰胺基，异构化和外消旋的天冬氨酰和天冬酰胺基残基代表了老化过程导致的蛋白质自发损伤的重要部分。这些残基的积累会导致蛋白质功能的丧失和随之而来的细胞功能的丧失。但是，自然界中几乎所有细胞都含有能够识别L-异天冬氨酰残基的主要受损形式的甲基转移酶，并且其中一些酶还可以识别外消旋的D-天冬氨酰残基。甲基酯化反应可以引发这些改变的残基向正常L-天冬氨酰形式的转化，尽管尚无证据表明L-天冬酰胺基形式可以再生。这种酶称为L-异天冬氨酸（D-天冬氨酸）O-甲基转移酶（EC 2.1.1.77），因此起蛋白质修复酶的作用。