HEME BIOSYNTHESIS IN BACTERIUM-PROTOZOON SYMBIOSES - ENZYMIC DEFECTS IN HOST HEMOFLAGELLATES AND COMPLEMENTAL ROLE OF THEIR INTRACELLULAR SYMBIOTES
HEME BIOSYNTHESIS IN BACTERIUM-PROTOZOON SYMBIOSES - ENZYMIC DEFECTS IN HOST HEMOFLAGELLATES AND COMPLEMENTAL ROLE OF THEIR INTRACELLULAR SYMBIOTES
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DOI：
10.1073/pnas.72.8.2979
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发表时间：
1975-01-01
影响因子：
11.1
通讯作者：
SASSA, S
中科院分区：
文献类型：
--
作者：
CHANG, KP;CHANG, CS;SASSA, S
通过酶实验、营养实验和同位素掺入实验，研究了鞭毛虫与胞内类杆菌共生过程中血红素的生物合成活性。对这种结合中的组成生物及其复合体分别进行了分析，以确定血鞭毛虫对氯化血红素需求的根本原因，以及共生体在避免两种分生生物对氯化血红素需求方面的作用。对无共生体鞭毛虫的营养研究表明，它们的生长至少需要0.1毫克/毫升的氯化血红素，可以被原卟啉IX取代，但不能被卟啉前体、β-氨基乙酰丙酸或卟啉原取代。在原卟啉IX存在的情况下，这些鞭毛虫将59Fe结合到血红素中，表明它们具有铁络合酶(EC 4.99.1.1)，这是血红素生物合成途径中的末端酶，催化铁插入到原卟啉IX中。在含有共生体的鞭毛虫中，连续培养在不含四吡咯化合物的特定介质中，可以用荧光光度法检测到血红素和卟啉，这表明血红素的生物合成。[14C]甘氨酸掺入血红素的研究表明，在含有共生体的鞭毛虫中的这一比率比在没有共生体的鞭毛虫中要高得多。尿卟啉原I合成酶的微量测定[EC 4.3.1.8；胆红素原解氨酶(聚合)]表明，在含有共生体的鞭毛虫中具有较高的比活性，在分离的共生体中更高，而在不含共生体的生物中基本上可以忽略不计。结论是，细菌共生体通过提供尿卟啉原I合成酶和可能先于亚铁螯合酶的其他酶来增强宿主鞭毛虫的血红素生物合成能力。
Heme biosynthetic activity in the symbiotic association involving crithidial flagellates and intracellular bacteroids was studied by enzymic, nutritional, and isotope incorporation experiments. Component organisms and their complexes in this association were analyzed separately to determine the underlying cause of the hemin requirement of hemoflagellates and the role of symbiotes in sparing this requirement of two crithidial species. Nutritional study of symbiote-free flagellates showed that their growth requires at least 0.1 mug/ml of hemin, which can be substituted by protoporphyrin IX, but not by the porphyrin precursors, delta-amino-levulinic acid or porphobilinogen. These flagellates, in the presence of protoporphyrin IX, incorporated 59Fe into heme, indicating that they possess ferrochelatase (EC 4.99.1.1), the terminal enzyme in the heme biosynthetic pathway, which catalyzes the insertion of iron into protoporphyrin IX. In symbiote-containing flagellates serially cultured in a defined medium free of tetrapyrrole compounds, heme and porphyrins can be detected by a fluorophotometric method, indicative of heme biosynthesis. Study of [14C]glycine incorporation into heme showed that the rate is much higher in symbiote-containing flagellates than in those without symbiotes. Microassay of uroporphyrinogen I synthase [EC 4.3.1.8; porphobilinogen ammonia-lyase (polymerizing)] revealed that the specific activity is high in symbiote-containing flagellates and higher still in isolated symbiotes, but essentially negligible in symbiote-free organisms. It is concluded that the bacterial symbiotes augment a very limited heme biosynthetic capacity of host flagellates by supplying uroporphyrinogen I synthase and perhaps other enzymes preceding ferrochelatase in the heme biosynthetic chain.