Esworthy R S, Chu F F, Paxton R J, Akman S, Doroshow J H
Department of Medical Oncology and Therapeutics Research, City of Hope National Medical Center, Duarte, CA 91010.
Arch Biochem Biophys. 1991 May 1;286(2):330-6. doi: 10.1016/0003-9861(91)90048-n.
Human plasma glutathione peroxidase was purified to homogeneity and partially sequenced. Overlapping peptide fragments from three endopeptidase digests permitted the determination of one sequence of 32 contiguous amino acids and one sequence of 23 contiguous amino acids. Five additional unique peptide sequences without obvious overlaps were obtained. The sequence of 32 amino acid residues aligns with positions 82-113 of human cytosolic glutathione peroxidase with nine mismatches without gaps or insertions. The sequence of 23 amino acid residues aligns with positions 157-178 with six mismatches and an insertion of one residue. Three additional peptide sequences with no obvious sequence homology to glutathione peroxidase can be aligned based on the sequence of a cDNA clone encoding plasma glutathione peroxidase that was isolated from a human placental library. The plasma enzyme is a homotetramer composed of 21-kDa subunits which cannot reduce phospholipid hydroperoxides. These results indicate that the plasma glutathione peroxidase is distinct from both the classical cytosolic enzyme and the monomeric phospholipid hydroperoxide glutathione peroxidase. Only a negligible amount of glutathione peroxidase activity was detected in bile, indicating that the liver exports plasma glutathione peroxidase exclusively to the circulation.
人血浆谷胱甘肽过氧化物酶被纯化至同质并进行了部分测序。来自三种内肽酶消化的重叠肽片段使得能够确定一段由32个连续氨基酸组成的序列和一段由23个连续氨基酸组成的序列。另外还获得了五个没有明显重叠的独特肽序列。32个氨基酸残基的序列与人类胞质谷胱甘肽过氧化物酶的82 - 113位对齐，有九个错配，没有间隙或插入。23个氨基酸残基的序列与157 - 178位对齐，有六个错配和一个残基插入。基于从人胎盘文库中分离出的编码血浆谷胱甘肽过氧化物酶的cDNA克隆的序列，可以对齐另外三个与谷胱甘肽过氧化物酶没有明显序列同源性的肽序列。血浆酶是由21 kDa亚基组成的同四聚体，不能还原磷脂氢过氧化物。这些结果表明，血浆谷胱甘肽过氧化物酶既不同于经典的胞质酶，也不同于单体磷脂氢过氧化物谷胱甘肽过氧化物酶。在胆汁中仅检测到可忽略不计的谷胱甘肽过氧化物酶活性，表明肝脏仅将血浆谷胱甘肽过氧化物酶输出到循环系统中。
