Human enzymes of xenobiotic metabolism

异生物质是外来化学物质，如药物、致癌物质和污染物。外来化合物在人体内以显著的化学方式代谢。这些代谢过程由细胞色素P450和谷胱甘肽转移酶等酶催化，在确定化学品的毒性作用方面至关重要。因此，它们不仅在生物化学中，而且在药理学和毒理学的相关学科中具有极大的兴趣。Josephy博士研究的中心主题是了解催化异生物质代谢的酶的生物化学，特别关注它们的蛋白质结构和催化功能。他的实验室将两种不同的生物技术结合在一起：细菌致突变性试验和重组蛋白表达。在约瑟夫博士实验室开发的新检测系统中，E.大肠杆菌被用来检测化学诱变剂，它们也被“教导”以与人类相同的方式代谢外来化学物质。也就是说，人类酶在细菌细胞内表达为重组蛋白。这种方法导致了越来越可靠和相关的有毒化学品的测定，它也提供了重要的人类酶的作用机制的见解。这些人类基因/酶中自然发生的变异的功能效应正在通过基因组测序项目被发现，目前正在研究中。另一种研究途径是在实验室中对具有改变的序列和催化活性的酶进行“进化”。研究计划的这一方面是通过随机诱变编码酶的基因，然后使用诱变性测定筛选突变体库并鉴定具有改变活性的突变体来进行的。

Human enzymes of xenobiotic metabolismXenobiotics are foreign chemicals such as drugs, carcinogens, and pollutants. Foreign compounds are metabolized in the human body in chemically remarkable ways. These metabolic processes, catalyzed by enzymes such as cytochrome P450 and glutathione transferase, can be crucial in determining the toxic effects of chemicals. Therefore, they are of great interest not only in biochemistry but also in the allied disciplines of pharmacology and toxicology. The central theme of Dr. Josephy's research is understanding the biochemistry of the enzymes that catalyze the metabolism of xenobiotics, with particular attention to their protein structures and catalytic functions. His lab. has brought together two different biotechnologies: bacterial mutagenicity assays and recombinant protein expression. In the new assay systems developed in Dr. Josephy's lab., E. coli bacteria are used to detect chemical mutagens, and they are also "taught" to metabolize foreign chemicals in the same ways that humans do. That is, human enzymes are expressed as recombinant proteins within the bacterial cells. This approach has led to increasingly reliable and relevant assays for toxic chemicals, and it also provides insight into the mechanisms of action of important human enzymes. The functional effects of naturally occurring variations in these human genes/enzymes, which are being discovered via genome sequencing projects, are now being studied. Another avenue of research is the "evolution", in the laboratory, of enzymes with altered sequences and catalytic activities. This aspect of the research program is pursued by randomly mutagenizing the gene encoding the enzyme, and then using the mutagenicity assay to screen libraries of mutants and identify ones with altered activities.