Dailey H A, Jones C S, Karr S W
Department of Microbiology, University of Georgia, Athens 30602.
Biochim Biophys Acta. 1989 Nov 9;999(1):7-11. doi: 10.1016/0167-4838(89)90021-6.
The ability of purified mouse ferrochelatase (protoheme ferro-lyase, EC 4.99.1.1) to bind and catalytically utilize a variety of porphyrins has been examined. In all, the kd, Km or Ki values for eleven different porphyrins, the Ki values for four metalloporphyrins and the kd values for two metalloporphyrins were determined. The data obtained demonstrate that mouse ferrochelatase binds a wide variety of porphyrins and metalloporphyrins with kd values ranging from 6 nM for N-methylprotoporphyrin to 1.08 microM for coproporphyrin III. However, the enzyme shows a degree of catalytic specificity for the substituents at the 2.4 positions and utilizes only proto-, hemato-, meso-, deutero-, 2,4-monohydroxy-ethylmonovinyl- and 2,4-monohydroxymethylmonovinyl deuteroporphyrin as substrates. The data show that the magnitude of the kd is not an accurate indicator of the ability of the porphyrin to serve as a substrate or inhibitor and, with the exception of N-methylprotoporphyrin, the size of the kd is several orders of magnitude less than that of the Km or Ki. Of the metalloporphyrins examined (Fe, Co, Zn and Sn) all inhibited ferrochelatase at micromolar concentrations, although tin protoporphyrin was the least effective. These data are discussed in terms of an active site model for mammalian ferrochelatase.
已对纯化的小鼠亚铁螯合酶（原卟啉亚铁裂解酶，EC 4.99.1.1）结合并催化利用多种卟啉的能力进行了研究。总共测定了11种不同卟啉的解离常数（kd）、米氏常数（Km）或抑制常数（Ki）值，4种金属卟啉的Ki值以及2种金属卟啉的kd值。所获得的数据表明，小鼠亚铁螯合酶能结合多种卟啉和金属卟啉，其kd值范围从N-甲基原卟啉的6 nM到粪卟啉III的1.08 μM。然而，该酶对2,4位的取代基表现出一定程度的催化特异性，仅将原卟啉、血卟啉、中卟啉、氘代卟啉、2,4-单羟基-乙基单乙烯基-和2,4-单羟甲基单乙烯基氘代卟啉用作底物。数据表明，kd的大小并非卟啉作为底物或抑制剂能力的准确指标，除了N-甲基原卟啉外，kd的大小比Km或Ki小几个数量级。在所检测的金属卟啉（铁、钴、锌和锡）中，尽管锡原卟啉效果最差，但所有金属卟啉在微摩尔浓度下均能抑制亚铁螯合酶。根据哺乳动物亚铁螯合酶的活性位点模型对这些数据进行了讨论。
