Andersson L A, Bylkas S A, Wilson A E
Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506, USA.
J Biol Chem. 1996 Feb 16;271(7):3406-12. doi: 10.1074/jbc.271.7.3406.
The identity of the non-extractable heme of mammalian lactoperoxidase (LPO) has remained unsolved for over 40 years. Accepted possibilities include a constrained heme b or an 8-thiomethylene-modified heme b. Recent studies of myeloperoxidase (MPO) (Fenna, R., Zeng, J., and Davey, C. (1995) Arch. Biochem. Biophys. 316, 653-656; Taylor, K. L., Strobel, F., Yue, K. T., Ram, P., Pohl, J., Woods, A. S., and Kinkade, J. M., Jr. (1995) Arch. Biochem. Biophys. 316, 635-642) suggest possible prosthetic group similarities between MPO and LPO. To address heme identity for LPO, we used comparative magnetic circular dichroism (MCD) spectroscopy of LPO versus myoglobin (Mb), horseradish peroxidase (HRP), and MPO. MCD spectra of native Fe3+-LPO and Fe3+-CN--LPO are approximately 10 nm red shifted from analogous forms of Mb and HRP, including the formate-Mb adduct. MCD spectra of native LPO and MPO are opposite in sign, and MCD spectra of their cyanoadducts also differ. These data indicate the LPO heme is distinct from heme b of Mb and HRP as well as from "heme m" of MPO. From this work and literature analysis, we suggest that the non-extractable "heme l" of LPO has the two vinyl groups of heme b but lacks the 2-sulfonium-vinyl linkage of heme m. The observed red shifts in LPO spectra may derive from ester linkages to protein as for MPO. Strong spectral analogies between LPO and mammalian peroxidases (e.g. from saliva, eosinophils, thyroid, intestine) indicate similar prosthetic heme moieties.
哺乳动物乳过氧化物酶（LPO）中不可提取血红素的身份问题在40多年来一直未得到解决。公认的可能性包括受限的血红素b或8-硫亚甲基修饰的血红素b。最近对髓过氧化物酶（MPO）的研究（Fenna, R., Zeng, J., and Davey, C. (1995) Arch. Biochem. Biophys. 316, 653 - 656; Taylor, K. L., Strobel, F., Yue, K. T., Ram, P., Pohl, J., Woods, A. S., and Kinkade, J. M., Jr. (1995) Arch. Biochem. Biophys. 316, 635 - 642）表明MPO和LPO之间可能存在辅基相似性。为了确定LPO的血红素身份，我们对LPO与肌红蛋白（Mb）、辣根过氧化物酶（HRP）和MPO进行了比较磁圆二色性（MCD）光谱分析。天然Fe3 + -LPO和Fe3 + -CN--LPO的MCD光谱比Mb和HRP的类似形式（包括甲酸-Mb加合物）大约红移10 nm。天然LPO和MPO的MCD光谱符号相反，它们氰基加合物的MCD光谱也不同。这些数据表明LPO血红素与Mb和HRP的血红素b以及MPO的“血红素m”不同。基于这项工作和文献分析，我们认为LPO中不可提取的“血红素l”具有血红素b的两个乙烯基，但缺少血红素m的2-锍-乙烯键。LPO光谱中观察到的红移可能如MPO一样源于与蛋白质的酯键。LPO与哺乳动物过氧化物酶（如来自唾液、嗜酸性粒细胞、甲状腺、肠道的过氧化物酶）之间强烈光谱相似性表明存在类似的辅基血红素部分。
