Colleran E M, Jones O T
Biochem J. 1973 May;134(1):89-96. doi: 10.1042/bj1340089.
A soluble cytochrome was isolated and purified from the slime mould Physarum polycephalum and identified as cytochrome c by room-temperature and low-temperature (77 degrees K) difference spectroscopy. A close similarity between P. polycephalum and mammalian cytochromes c was suggested by a comparison of the initial rates of oxidation of both proteins by mammalian mitochondria. This similarity was further emphasized by redox titrations and gel-electrophoretic studies which indicated that P. polycephalum cytochrome c has an oxidation-reduction midpoint potential of +257mV at pH7.0 and a molecular weight of 12500+/-1500 (mean+/-maximum deviation for a set of six measurements). P. polycephalum exhibits an absolute requirement for protohaemin for growth. The (59)Fe-labelled haemin was prepared by chemical synthesis from protoporphyrin. The purified product had a specific radioactivity of 0.8+/-0.02muCi/mol. Growth of P. polycephalum in the presence of [(59)Fe]haemin resulted in the incorporation of (59)Fe into the plasmodial cytochrome c. The specific radioactivity of the cytochrome c haem was 0.36+/-0.02muCi/mol. The high specific radioactivity of the cytochrome haem indicates that synthesis of the holoenzyme must proceed by direct attachment of haem to the apoprotein rather than by the intermediate formation of a protoporphyrinogen-apoprotein complex. The observed decrease in the specific radioactivity of the haem group is attributed to exchange of the (59)Fe with unlabelled iron in the plasmodia either before or during attachment of the haem group to the apoprotein.
从多头绒泡菌中分离并纯化出一种可溶性细胞色素，通过室温及低温（77K）差光谱法鉴定为细胞色素c。通过比较哺乳动物线粒体对这两种蛋白质的初始氧化速率，发现多头绒泡菌与哺乳动物细胞色素c有密切相似性。氧化还原滴定和凝胶电泳研究进一步强调了这种相似性，结果表明多头绒泡菌细胞色素c在pH7.0时的氧化还原中点电位为+257mV，分子量为12500±1500（一组六次测量的平均值±最大偏差）。多头绒泡菌生长绝对需要原血红素。（59）Fe标记的血红素由原卟啉化学合成制备。纯化产物的比放射性为0.8±0.02μCi/mol。在[（59）Fe]血红素存在下多头绒泡菌的生长导致（59）Fe掺入原质团细胞色素c中。细胞色素c血红素的比放射性为0.36±0.02μCi/mol。细胞色素血红素的高比放射性表明全酶的合成必须通过血红素直接与脱辅基蛋白结合进行，而不是通过原卟啉原 - 脱辅基蛋白复合物的中间形成。观察到的血红素基团比放射性的降低归因于在血红素基团与脱辅基蛋白结合之前或期间，（59）Fe与原质团中未标记的铁发生交换。
