d-Aspartate oxidase (DDO) is a flavin adenine dinucleotide (FAD)-containing flavoprotein that stereospecifically acts on acidic d-amino acids (i.e., free d-aspartate and d-glutamate). Mammalian DDO, which exhibits higher activity toward d-aspartate than d-glutamate, is presumed to regulate levels of d-aspartate in the body and is not thought to degrade d-glutamate in vivo. By contrast, three DDO isoforms are present in the nematode Caenorhabditis elegans, DDO-1, DDO-2, and DDO-3, all of which exhibit substantial activity toward d-glutamate as well as d-aspartate. In this study, we optimized the Escherichia coli culture conditions for production of recombinant C. elegans DDO-1, purified the protein, and showed that it is a flavoprotein with a noncovalently but tightly attached FAD. Furthermore, C. elegans DDO-1, but not mammalian (rat) DDO, efficiently and selectively degraded d-glutamate in addition to d-aspartate, even in the presence of various other amino acids. Thus, C. elegans DDO-1 might be a useful tool for determining these acidic d-amino acids in biological samples.

中文翻译：

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秀丽隐杆线虫的d-天冬氨酸氧化酶的生化特性：其在测定生物样品中游离d-谷氨酸中的潜在用途。

d-天冬氨酸氧化酶（DDO）是一种含有黄素腺嘌呤二核苷酸（FAD）的黄素蛋白，其立体定向作用于酸性d-氨基酸（即游离的d-天冬氨酸和d-谷氨酸）。哺乳动物DDO对d-天冬氨酸的活性高于d-谷氨酸，据推测可调节体内d-天冬氨酸的水平，并且不认为其会在体内降解d-谷氨酸。相比之下，线虫秀丽隐杆线虫中存在三种DDO同工型，即DDO-1，DDO-2和DDO-3，它们均对d-谷氨酸和d-天冬氨酸具有实质性活性。在这项研究中，我们优化了大肠杆菌的培养条件，以生产重组秀丽隐杆线虫DDO-1，纯化了该蛋白质，并表明它是一种具有非共价但紧密连接的FAD的黄素蛋白。此外，秀丽隐杆线虫DDO-1，但不是哺乳动物（大鼠）DDO，即使存在多种其他氨基酸，除d-天门冬氨酸外，还可以有效和选择性地降解d-谷氨酸。因此，秀丽隐杆线虫DDO-1可能是确定生物样品中这些酸性d-氨基酸的有用工具。