A hemoglobin-like protein from Protozoan ciliates : Its structure and function

梨形四膜虫的一种肌红蛋白样蛋白由121个氨基酸残基组成，包括血红素部分在内的分子质量为14,343道尔顿。这比抹香鲸肌红蛋白小了32个残基，与其他肌红蛋白和血红蛋白在序列上没有明显的相似性。为了研究这种独特的蛋白质的光谱和稳定性，我们通过在Sephadex G-50上使用凝胶过滤，然后使用cm -纤维素色谱法，直接从填充细胞中分离出大量的天然氧形式。结果表明，四膜虫氧肌红蛋白在0.1M缓冲液中，在25‰的温度下，在pH4-12的大范围内具有良好的抗氧化性，其速率常数与抹香鲸MbO_2的速率常数基本一致。因此，我们得出结论，四膜虫肌红蛋白可以像哺乳动物肌红蛋白一样稳定地结合分子氧，尽管它的结构非常收缩，可能是由于大量的氨基酸缺失。

A myoglobin-like protein from Tetrahymena pyriformis is composed of 121 amino acid residues with a molecular mass of 14,343 daltons including the heme moiety. This is much smaller than sperm whale myoglobin by 32 residues and shows no notable degree of sequence similarity with other myoglobins and hemoglobins. In order to examine this unique protein for its spectral and stability properties, we have isolated a large amount of its native oxy-form directly from the packed cells by using gel filtration on Sephadex G-50 followed by CM-cellulose chromatography. As a result, Tetrahymena oxymyoglobin was found to be quite resistant against the autoxidation reaction over a wide range of pH4-12 in 0.1M buffer at 25ﾟC,its rate-constant being almost the same as that of sperm whale MbO_2. We therefore conclude that Tetrahymena myoglobin can bind molecular oxygen as stably as mammalian myoglobins can do, in spite of its very contracted structure probably due to a large number of amino acid deletions.