Dickerson A G
Biochem J. 1972 Sep;129(2):263-72. doi: 10.1042/bj1290263.
Evidence suggests that sucrose is the main carbon source for growth of Claviceps spp. in the parasitic condition. The sucrose acts as substrate for an active beta-fructofuranosidase, produced by the fungus, which in the first instance converts the disaccharide into glucose and an oligofructoside. In this way, 50% of the glucose, supplied as sucrose, is made available to the parasite for assimilation. Subsequent action of the enzyme on both sucrose and the oligofructoside leads to the release of more glucose and the formation of additional oligosaccharides. The structures of the main oligosaccharides formed have been elucidated and the interactions of each compound studied. In experiments with purified enzyme in vitro the interaction of the oligosaccharides is rapid but in culture they are assimilated only slowly; in each case some free fructose is liberated. Free fructose is not assimilated in the presence of glucose and, further, inhibits growth at concentrations which might be expected to occur in the parasitic condition. A dual role has been suggested for the enzyme, with sucrose as substrate, in which glucose is made available to the growing parasite, while at the same time transfer of the fructose to form oligosaccharides prevents it from accumulating at inhibitory concentrations. Ultimately, when glucose becomes limiting, the fungus will adapt to fructose assimilation.
有证据表明，蔗糖是麦角菌属在寄生状态下生长的主要碳源。蔗糖作为该真菌产生的一种活性β-呋喃果糖苷酶的底物，首先将二糖转化为葡萄糖和一种低聚果糖苷。通过这种方式，以蔗糖形式提供的葡萄糖中有50%可供寄生物同化利用。该酶随后对蔗糖和低聚果糖苷的作用导致释放出更多葡萄糖并形成额外的寡糖。已阐明了所形成的主要寡糖的结构，并研究了每种化合物的相互作用。在体外使用纯化酶进行的实验中，寡糖的相互作用很快，但在培养物中它们的同化作用却很缓慢；在每种情况下都会释放出一些游离果糖。在有葡萄糖存在时，游离果糖不能被同化，而且，在可能预期会出现在寄生状态下的浓度时，它会抑制生长。有人提出，以蔗糖为底物的这种酶具有双重作用，即向生长中的寄生物提供葡萄糖，同时将果糖转移以形成寡糖可防止其在抑制浓度下积累。最终，当葡萄糖变得有限时，真菌将适应果糖同化。
