BIOCHEMISTRY AND METABOLISM OF GIARDIA
BIOCHEMISTRY AND METABOLISM OF GIARDIA
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DOI：
10.1111/j.1550-7408.1989.tb01073.x
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发表时间：
1989-03-01
期刊：
影响因子：
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通讯作者：
LINDMARK, DG
中科院分区：
文献类型：
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作者：
JARROLL, EL;MANNING, P;LINDMARK, DG
蓝氏贾第鞭毛虫是一种耐氧厌氧菌，在氧气存在下通过黄素、铁硫蛋白介导的电子传递系统进行呼吸。葡萄糖似乎是通过Embden-Meyerhof-Parmas和己糖单磷酸途径分解代谢的唯一糖，并且能量由底物水平磷酸化产生。底物被不可沉淀的酶不完全氧化为CO2、乙醇和乙酸盐。缺乏肌苷、次黄嘌呤、黄嘌呤、甲酸或甘氨酸掺入核苷酸中表明缺乏从头嘌呤合成。只有腺嘌呤、腺苷、鸟嘌呤和鸟苷被挽救，并且没有检测到这些嘌呤的相互转化。这些嘌呤和它们的核苷的补救是通过腺嘌呤磷酸核糖基转移酶、腺苷水解酶、鸟苷磷酸核糖基转移酶和鸟嘌呤水解酶完成的。通过缺乏碳酸氢盐、乳清酸盐和天冬氨酸盐掺入核苷酸中，以及缺乏可检测水平的从头嘧啶合成酶，证实了从头嘧啶合成的缺乏。补救似乎是通过尿嘧啶磷酸核糖转移酶、尿苷磷酸转移酶、胞苷脱氨酶、胞苷水解酶、胞嘧啶磷酸核糖转移酶和胸苷磷酸转移酶的作用完成的。三磷酸胞苷合成酶可将尿嘧啶核苷酸转化为胞嘧啶核苷酸，但未检测到胸苷酸合成酶和二氢叶酸还原酶活性。嘧啶核苷（可能还有嘧啶）的摄取似乎是通过载体介导的转运完成的，尿苷和胞苷摄取的共同位点与胸苷的位点不同。胸腺嘧啶似乎不被纳入核苷酸池。贾第虫滋养体似乎依赖于预先形成的脂质，而不是从头合成它们。主要脂质包括磷脂酰胆碱、磷脂酰乙醇胺、磷脂酰甘油、鞘磷脂、固醇（可能是胆固醇）以及单、二和三酰甘油酯。G.从沙鼠中分离出的蓝氏贾第鞭毛虫G.从小鼠分离的鼠滋养体与从G.体外培养的兰氏藻。对G.已经显示出兰氏体局限于单一溶酶体样颗粒群，在蔗糖中具有约1.15平衡密度。与内阿米巴和毛滴虫的滋养体相反，贾第虫滋养体似乎缺乏大多数碳水化合物裂解水解酶。钙调素在G. Lamblia滋养体，并且它似乎具有与从其它真核细胞分离的钙调蛋白相似的性质。
Giardia lamblia, an aerotolerant anaerobe, respires in the presence of oxygen by a flavin, iron-sulfur protein-mediated electron transport system. Glucose appeared to be the only sugar catabolized by the Embden-Meyerhof-Parmas and hexose monophosphate pathways, and energy is produced by substrate level phosphorylation. Substrates are incompletely oxidized to CO2, ethanol and acetate by nonsedimentable enzymes. The lack of incorporation of inosine, hypoxanthine, xanthine, formate or glycine into nucleotides indicates an absence of de novo purine synthesis. Only adenine, adenosine, guanine and guanosine are salvaged, and no interconversion of these purines was detected. Salvage of these purines and their nucleosides is accomplished by adenine phosphoribosyltransferase, adenosine hydrolase, guanosine phosporibosyltransferase and guanine hydrolase. The absence of de novo pyrimidine synthesis was confirmed by the lack of incorporation of bicarbonate, orotate and aspartate into nucleotides, and by the lack of detectable levels of the enzymes of de novo pyrimidine synthesis. Salvage appears to be accomplished by the action of uracil phosphoribosyltranferase, uridine phosphotransferase, cytidine deaminase, cytidine hydrolase, cytosine phosphoribosyltransferase and thymidine phosphotransferase. Nucleotides of uracil may be converted to nucleotides of cytosine by cytidine triphosphate synthetase, but thymidylate synthetase and dihydrofolate reductase activities were not detected. Uptake of pyrmidine nucleosides, and perhaps pyrimidines, appears to be accomplished by carrier-mediated transport, and the common site for uptake of uridine and cytidine is distinct from the site for thymidine. Thymine does not appear to be incorporated into nucleotide pools. Giardia trophozoites appear to rely on preformed lipids rather than synthesizing them de novo. Major lipids include phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, sphingomyelin, sterol (probably cholesterol) and mono-, di- and triactylglycerides. The lipid composition of the cysts of G. lamblia isolated form gerbils and G. muris isolated from mice are similar to those obtained from the trophozoites of G. lamblia grown in vitro. The activities of several hydrolases of G. lamblia have been shown to be confined to a single lysosome-like particle population with an equilibrium density of approximately 1.15 in sucrose. Contrary to the trophozoites of Entamoeba and the trichomonads, Giardia trophozoites appear to lack most carbohydrate splitting hydrolases. Calmodulin has been reported in G. lamblia trophozoites, and it appears to have properties similar to the calmodulin isolated from other eucaryotic cells.