An increasing body of biochemical and genetic evidence suggests that inorganic pyrophosphate (PPi) plays an important role in protist bioenergetics. In these organisms, two types of inorganic pyrophosphatases [EC 3.6.1.1, namely soluble PPases (sPPases) and proton-translocating PPases (H⁺-PPases)] that hydrolyse the PPi generated by cell anabolism, thereby replenishing the orthophosphate pool needed for phosphorylation reactions, are present in different cellular compartments. Photosynthetic and heterotrophic protists possess sPPases located in cellular organelles (plastids and mitochondria), where many anabolic and biosynthetic reactions take place, in addition to H⁺-PPases, which are integral membrane proteins of the vacuolysosomal membranes and use the chemical energy of PPi to generate an electrochemical proton gradient useful in cell bioenergetics. This last category of proton pumps was considered to be restricted to higher plants and some primitive photosynthetic bacteria, but it has been found recently in many protists (microalgae and protozoa) and bacteria, thus indicating that H⁺-PPases are much more widespread than previously thought. No cytosolic sPPase (in bacteria, fungi and animal cells) has been shown to occur in these lower eukaryotes. The widespread occurrence of these key enzymes of PPi metabolism among evolutionarily divergent protists strongly supports the ancestral character of the bioenergetics based on this simple energy-rich compound, which may play an important role in survival under different biotic and abiotic stress conditions.

中文翻译：

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光合和异养生物中无机焦磷酸盐生物能的酶系统：残留物还是代谢基石？

越来越多的生化和遗传证据表明，无机焦磷酸盐（PPi）在有机生物能学中起着重要作用。在这些生物中，有两种类型的无机焦磷酸酶[EC 3.6.1.1，即可溶性PPase（sPPase）和质子移位PPase（H ⁺ -PPases）]，它们水解细胞合成代谢产生的PPi，从而补充磷酸化所需的正磷酸盐库反应存在于不同的细胞室中。光合和异养生物质子体具有位于细胞器（质体和线粒体）中的sPPase，除H ⁺外，还发生许多合成代谢和生物合成反应-PPase是空泡体膜的完整膜蛋白，利用PPi的化学能产生可用于细胞生物能学的电化学质子梯度。质子泵的最后一类被认为仅限于高等植物和一些原始的光合细菌，但最近在许多生物（微藻和原生动物）和细菌中被发现，因此表明H ⁺-PPases比以前认为的要广泛得多。在这些低等的真核生物中未发现胞质sPPase（在细菌，真菌和动物细胞中）发生。PPi代谢的这些关键酶在进化上不同的原生生物中广泛存在，有力地支持了基于这种简单的富含能量的化合物的生物能学的祖先特性，这可能在不同生物和非生物胁迫条件下的存活中起重要作用。