Polyphenol curcumin, a yellow pigment, derived from the rhizomes of a plant (
Curcuma longa
Linn) is a natural antioxidant exhibiting a variety of pharmacological activities and therapeutic properties. It has long been used as a traditional medicine and as a preservative and coloring agent in foods. Here, curcumin-converting microorganisms were isolated from human feces, the one exhibiting the highest activity being identified as
Escherichia coli
. We are thus unique in discovering that
E. coli
was able to act on curcumin. The curcumin-converting enzyme was purified from
E. coli
and characterized. The native enzyme had a molecular mass of about 82 kDa and consisted of two identical subunits. The enzyme has a narrow substrate spectrum, preferentially acting on curcumin. The microbial metabolism of curcumin by the purified enzyme was found to comprise a two-step reduction, curcumin being converted NADPH-dependently into an intermediate product, dihydrocurcumin, and then the end product, tetrahydrocurcumin. We named this enzyme “NADPH-dependent curcumin/dihydrocurcumin reductase” (CurA). The gene (
curA
) encoding this enzyme was also identified. A homology search with the BLAST program revealed that a unique enzyme involved in curcumin metabolism belongs to the medium-chain dehydrogenase/reductase superfamily.
多酚姜黄素是一种来源于植物根茎(姜黄)的黄色色素,是一种天然抗氧化剂,展现出多种药理活性和治疗特性。长期以来,它一直被用作传统药物,以及食品的防腐剂和着色剂。在这里,从人类粪便中分离出了转化姜黄素的微生物,其中表现出最高活性的被鉴定为大肠杆菌。因此,我们发现大肠杆菌能够作用于姜黄素是独特的。从大肠杆菌中纯化并表征了转化姜黄素的酶。原生酶的分子量约为82 kDa,由两个相同的亚基组成。该酶具有狭窄的底物谱,优先作用于姜黄素。通过纯化酶对姜黄素的微生物代谢发现,包括一个两步还原过程,姜黄素首先以NADPH为辅助转化为一个中间产物,二氢姜黄素,然后形成最终产物四氢姜黄素。我们将这种酶命名为“NADPH依赖的姜黄素/二氢姜黄素还原酶”(CurA)。还鉴定了编码这种酶的基因(curA)。通过BLAST程序进行同源搜索,发现参与姜黄素代谢的独特酶属于中链脱氢酶/还原酶超家族。