Lactoperoxidase (LPO) is a heme containing oxido-reductase enzyme. It is secreted from mammary, salivary, lachrymal and mucosal glands. It catalyses the conversion of thiocyanate into hypothiocyanate and halides into hypohalides. LPO belongs to the superfamily of mammalian heme peroxidases which also includes myeloperoxidase (MPO), eosinophil peroxidase (EPO) and thyroid peroxidase (TPO). The heme prosthetic group is covalently linked in LPO through two ester bonds involving conserved residues Glu258 and Asp108. It was isolated from colostrum of yak (Bos grunniens), purified to homogeneity and crystallized using ammonium iodide as a precipitating agent. The crystals belonged to monoclinic space group P2₁ with cell dimensions of a = 53.91 Å, b = 78.98 Å, c = 67.82 Å and β = 92.96°. The structure was determined at 1.55 Å resolution. This is the first structure of LPO from yak. Also, this is the highest resolution structure of LPO determined so far from any source. The structure determination revealed that three segments (Ser1–Cys15), (Thr117–Asn138) and (Cys167–Leu175) were disordered and formed one surface of LPO structure. In the substrate binding site, the iodide ions were observed in three subsites which are formed by (1) heme moiety and residues, Gln105, Asp108, His109, Phe113, Arg255, Glu258, Phe380 and Phe381, (2) residues, Asn230, Lys232, Pro236, Cys248, Phe254, Phe381 and Pro424 and (3) residues, Ser198, Leu199 and Arg202. The structure determination also revealed that the side chain of Phe254 was disordered. It was observed to adopt two conformations in the structures of LPO.

乳过氧化物酶（LPO）是一种含有血红素的氧化还原酶。它从乳腺，唾液，泪腺和粘膜腺体分泌。它催化硫氰酸盐向次硫氰酸盐的转化，以及卤化物向次卤化物的转化。LPO属于哺乳动物血红素过氧化物酶的超家族，还包括髓过氧化物酶（MPO），嗜酸性粒细胞过氧化物酶（EPO）和甲状腺过氧化物酶（TPO）。血红素修复基团在LPO中通过两个酯键共价连接，涉及保守残基Glu258和Asp108。从from牛（Bos grunniens）的初乳中分离出来，纯化至均质，并使用碘化铵作为沉淀剂进行结晶。晶体属于单斜空间群P2 ₁像元尺寸为a = 53.91Å，b = 78.98Å，c = 67.82Å和β= 92.96°。确定结构的分辨率为1.55Å。这是来自ak牛的LPO的第一个结构。此外，这是迄今为止尚未确定的LPO的最高分辨率结构。结构确定表明，三个片段（Ser1-Cys15），（Thr117-Asn138）和（Cys167-Leu175）无序，并形成了LPO结构的一个表面。在底物结合位点，在三个亚位点观察到碘离子，这些亚位点由（1）血红素部分和残基Gln105，Asp108，His109，Phe113，Arg255，Glu258，Phe380和Phe381形成，（2）残基，Asn230，Lys232 ，Pro236，Cys248，Phe254，Phe381和Pro424，以及（3）残基，Ser198，Leu199和Arg202。结构确定还显示Phe254的侧链是无序的。