STUDY OF FUNGAL METABOLISM BY 13C NMR

机会性真菌白色念珠菌的二态性，即酵母菌与菌丝的转化，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理知之甚少。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，来比较酵母和菌丝体两种细胞形式对葡萄糖和其他碳源的代谢。我们设计了一个原始的实验系统，利用新分离的白色念珠菌形态突变体作为菌丝体形式。通过这种方法，我们能够在相同的培养条件下制备酵母和菌丝细胞。首先，将2-13C或1-13C葡萄糖喂给两种细胞形式。结果发现，酵母型（野生型）产生的多元醇之一阿拉伯糖醇在菌丝体（突变型）中的积累急剧减少，尽管葡萄糖的消耗速率大致相同。通过分析两种细胞形式中2-13C或1-13C醋酸盐的代谢，证实了这一发现。此外，从该突变体分离出的逆转体（酵母）中阿拉糖醇的正常积累和另一形态突变体（菌丝体）中阿拉糖醇产量的减少表明代谢变化与形态变化有关。阿拉伯糖醇产量的减少意味着为许多生物合成反应提供NADPH还原力的单磷酸己糖分流活性低。细胞内NADPH水平与细胞形态的关系有待进一步研究。

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.