Transfer of invertase production from a wild strain of Escherichia coli.

A wild type strain of E. coli which produced an invertase capable of hydrolysing sucrose and raffinose transmitted this ability at high frequency to a recipient strain. E. coli C. The ability to ferment both sucrose and raffinose was lost both in the wild type parent and recombinant strains by treatment with ethidium bromide.

Carbon assimilation by Claviceps purpurea growing as a parasite.

Carbon assimilation by Claviceps purpurea, growing as a parasite on cereals, has been investigated by supplying the host plant with 14CO2 in a closed system. The presence of the pathogen induced the plant to exude photosynthate which contained high levels of sucrose. During the period of 14CO2 supply, 14C was incorporated into the sucrose and so the path of carbon into the parasite could be traced. Hexoses, derived by the action of the fungal sucrase on sucrose, were assimilated by the pathogen and largely converted into polyols - mainly mannitol and, to a lesser extent, trehalose. The rate of carbohydrate metabolism decreased with maturation of the ergot, and also showed qualitative differences between the basal and apical regions of the ergot which were probably a function of nutrient supply.

Metabolism of the germinating sclerotium of Claviceps purpurea.

The concentration of free amino acids, particularly alanine, altered as stromata developed on germinating sclerotia. Lipid reserves in the sclerotium provided the principal carbon and energy source, and the nutrients required for stomatal growth appeared to be provided by the sclerotial tissues immediately beneath the point of attachment of the stoma. Alkaloid did not disappear from the sclerotia during germination. Very high levels of polyol, particularly mannitol, were attained in the stromata as germination progressed; the synthesis of polyol was usually accompanied by that of soluble sugars, notably glucose. In an attempt to ascertain the role of mannitol in germination, the relationship between polyol and soluble sugars was investigated in excised stromata after their submergence in buffered media containing a variety of soluble carbohydrates. Mannitol was synthesized under these conditions by way of phosphorylated intermediates, and chiefly in the capitulum, after rapid, and probably passive, absorption of the exogenously supplied sugar. The tissues equilibrated rapidly with the supplied carbohydrate, whose concentration was maintained by further uptake whilst mannitol was being synthesized. The concentrations of assimilated glucose and synthesized mannitol tended toward the same value during incubation and the results suggested that the synthesis was compartmentalized within the stromata. Very little exogenously supplied mannitol was assimilated.

A -D-fructofuranosidase from Claviceps purpurea.

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.

The metabolism of fructose polymers in plants. Transfructosylation in tubers of Helianthus tuberosus L.

1. A transfructosylase was separated from Jerusalem artichoke-tuber extracts. The partially purified enzyme was practically free from fructosans and its specific activity was increased more than sevenfold. 2. The enzyme was highly specific for terminal beta-(2-->1')-linked fructofuranosyl residues. 3. The most active donor found was 1(F)-fructosylsucrose, which had about five times the reactivity of the next higher homologues (degree of polymerization 4-6); (1-fructosyl)(2)fructose was intermediate in reactivity; sucrose was inactive. 4. Sucrose, and polymers of high degree of polymerization (>20), were the most efficient acceptors for transferred fructosyl residues of the compounds tested. 5. A variety of transferase activities appeared to be catalysed by the enzyme, namely, dismutation (;self-transfer') giving rise to a series of polymers ranging in degree of polymerization both above and below that of the original substrate, transfer to polymer giving rise to limited quantities of higher polymers, and transfer to sucrose; in the last case 1(F)-fructosylsucrose/sucrose transfer (resulting in exchange labelling of sucrosyl groups) was used to investigate the mechanism of the reaction more fully. 6. Since fructose transfer can be demonstrated in the living plant tissue, the inter-relationships of the various activities and their significance in fructosan metabolism are discussed.