On the very rapid enhancement by D2O of the temperature-tolerance of adult Drosophila.

Deuterium oxide, D(2)O, increases the temperature-tolerance of Drosophila pseudoobscura when it is administered to adult flies as a sucrose solution. The effect is very rapidly exerted; it is detected within 10 min after the flies have a brief (10 min) opportunity to drink. This increased resistance to heat-death surely implies an increased resistance of macromolecules to thermal denaturation. D(2)O is known to exert such an effect on in vitro protein solutions. The speed with which the increased stability develops clearly implicates a solvent action of D(2)O, and is most easily understood if the effect is traceable to enhancement of the hydrophobic interactions which contribute to conformational stability. The increased strength of deuterated hydrogen bonds cannot be excluded however. The possible bearing of these results on the hypothesis that D(2)O always increases the period of circadian oscillations by "diminishing the apparent temperature" is briefly considered.