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H G Floss

Publications and source records attributed to H G Floss.

At least 127 records · Page 7Linked to original sources
PubMed1973

Some characteristics of tryptophan uptake in Claviceps species.

Tryptophan serves as a precursor for the biosynthesis of alkaloids in the ergot fungus, Claviceps purpurea (Fries) Tulasne, and also is believed to act as an inducer of the enzymes necessary for alkaloid production. The characteristics of the transport system responsible for the accumulation of tryptophan in ergot mycelium were investigated, with the goal of clarifying the complex relationships among tryptophan uptake, size of the free intracellular pool of tryptophan, and alkaloid production. The characteristics of tryptophan uptake were studied by pulse feeding radioactively labeled tryptophan to cultures of Claviceps species, strain SD-58, which represented a variety of ages and nutritional states. Tryptophan accumulation in strain SD-58 is mediated by an energy-requiring system which exhibits specificity for neutral aromatic and aliphatic l-amino acids, is pH and temperature dependent, and shows saturation at high substrate concentrations. Tryptophan transport is a function of the intracellular concentration of free tryptophan, the nitrogen deficiency of the mycelium, the rate of growth, and alkaloid production, which were measured in Claviceps strain SD-58 growth in several culture media, some of which promoted alkaloid production and some of which did not. The results indicate that the initial velocity of tryptophan transport is not directly related to alkaloid production.

Alkaloids↗
PubMed1972

Physiological studies on ergot: further studies on the induction of alkaloid synthesis by tryptophan and its inhibition by phosphate.

The failure of l-leucine to stimulate ergot alkaloid production in a synthetic medium indicates that the previously observed stimulation by tryptophan and tryptophan analogues does not merely represent a nutritional effect. Tryptophan, but not mevalonate or 5-methyltryptophan, is able to overcome the inhibition of alkaloid synthesis by high levels of inorganic phosphate. Therefore, high phosphate levels seem to limit the synthesis of tryptophan; they may, in addition, prevent induction of alkaloid synthesis by preventing accumulation of tryptophan. Experiments which indicate a 2- to 3-fold temporary increase of intracellular free tryptophan and a 20- to 25-fold increase of tryptophan synthetase activity during the transition period between growth and alkaloid production phase are in agreement with the previously postulated induction of alkaloid synthesis by tryptophan. The latter experiments also indicate 4- to 6-fold repression of this enzyme by tryptophan.

Amino Acids↗