Elder G H, Urquhart A J
IARC Sci Publ. 1986(77):441-8.
Immunoreactive and catalytic uroporphyrinogen decarboxylase has been measured in the livers of rodents made porphyric by hexachlorobenzene (HCB). Catalytic activity decreased progressively as porphyria developed but was not accompanied by a fall in the concentration of immunoreactive enzyme protein. These findings suggest that HCB specifically inactivates uroporphyrinogen decarboxylase without affecting those regions of the molecule that determine its antigenic activity and without increasing its rate of catabolism. In vitro, uroporphyrin-catalysed photoinactivation of uroporphyrinogen decarboxylase was similarly unaccompanied by loss of immunoreactivity, whereas reaction of sulfhydryl groups with N-ethylmaleimide led to loss of both catalytic activity and immunoreactivity. These results suggest that, if HCB causes chronic porphyria by modifying sulfhydryl groups in the enzyme, the effect is restricted to catalytic or substrate-binding sites.
在通过六氯苯（HCB）诱导产生卟啉症的啮齿动物肝脏中，已对免疫反应性和催化性尿卟啉原脱羧酶进行了测定。随着卟啉症的发展，催化活性逐渐降低，但免疫反应性酶蛋白的浓度并未下降。这些发现表明，HCB特异性地使尿卟啉原脱羧酶失活，而不影响该分子中决定其抗原活性的区域，也不增加其分解代谢速率。在体外，尿卟啉催化的尿卟啉原脱羧酶光失活同样未伴随免疫反应性的丧失，而巯基与N - 乙基马来酰亚胺的反应导致催化活性和免疫反应性均丧失。这些结果表明，如果HCB通过修饰酶中的巯基导致慢性卟啉症，其作用仅限于催化或底物结合位点。
