STUDY OF FUNGAL METABOLISM BY 13C NMR

机会性真菌白色念珠菌的二形性，即酵母-菌丝转化，具有特别重要的医学意义。因为它被认为与念珠菌感染的发病机制有关。然而，人们对这一现象的机制知之甚少。为了在代谢方面解决这一问题，我们试图通过一种新型的分析方法13C NMR来比较葡萄糖和其他碳源在酵母和菌丝体两种细胞形态中的代谢。为此，我们设计了一套新颖的实验系统，使用新分离的白念珠菌形态突变株作为菌丝体。通过这种方法，我们能够制备在相同培养条件下生长的酵母和菌丝体细胞。首先，将2-13C或1-13C葡萄糖分别喂入两种细胞形态。研究发现，酵母形态(野生型)产生的多元醇之一阿拉伯醇在菌丝体(突变体)中的积累量急剧减少，而葡萄糖的消耗速度大致相同。通过分析2-13C或1-13C醋酸酯在两种细胞形态中的代谢，证实了这一发现。此外，突变株(酵母)中阿拉伯醇的正常积累和另一个形态突变株(菌丝体)中阿拉伯醇产量的减少表明代谢变化与形态变化有关。阿拉伯醇产量的减少意味着己糖单磷酸分流活性低，该分流为许多生物合成反应提供NADPH还原动力。该真菌的细胞NADPH水平与细胞形态之间的关系是下一个问题。

Dimorphism, the yeast-mycelium conversion, of the opportunistic fungus Candida albicans is of particular medical importance. Because it has been thought to have relevance to the pathogenesis of Candida infection. However, only a little was known about the mechanism of this phenomenon. To attack this problem in the aspect of metabolism, we attempted to compare the metabolism of glucose and other carbon sources between the two cell forms, yeast and mycelium, by a new type of analytical method, 13C NMR.We devised an original experimental system by employing newly isolated morphological mutants of C.albicans as a mycelium form for this purpose. By this, we were able to prepare both yeast and mycelium cells grown under the same cultural condition. First, 2-13C or 1-13C glucose was fed to both cell forms. It was found that the accumulation of arabitol, one of polyols produced by yeast form (wild type), drastically decreased in mycelium (mutant), although the consumption rate of glucose was roughly equal. This finding was confirmed by analysing the metabolism of 2-13C or 1-13C acetate in both cell forms. Furthermore, normal accumulation of arabitol in revertant (yeast) isolated from the mutant and decrease of arabitol production in another morphological mutant (mycelium) suggest the correlation of the metabolic change to the morphological change. Decrease of arabitol production implies the low activity of hexose monophosphate shunt, which supplies NADPH,reducing power, to many biosynthetic reactions. Relationship between cellular NADPH level and cell morphology of this fungus is next question.