No abstract

The hydrogen isotopic content of an animal's food, not water, determines that animal's hydrogen isotopic content. Liver and muscle tissue from mice reared on a diet such that the ratio of deuterium to hydrogen (DIH) of their food and water was kept constant, have the same average D/H ratio as the food source. In a simple, natural population of snails and their possible algal diets, Littorina obtusata (northern Atlantic intertidal snails that feed almost exclusively on the brown alga Fucus vesiculosus) has the same D/H ratio as Fucus vesiculosis and not that of the other algae available to the snails.

Isotope effects, studied with precision isotope ratio mass (1). Additional fractionation of hydrogen isotopes occurs during biosynthesis. Fatty acids, hydrocarbons, sterols, and other lipids have much lower deuterium concentrations than the organically bonded hydrogen of the total organism (3, 7). This second fractionation step is believed to occur before or during the formation of acetyl-CoA (1).To understand further the biochemical reactions fractionating hydrogen isotopes in plants and to determine their inter-relationships, with the goal of detecting steps that regulate hydrogen metabolism, the growth conditions of the versatile alga, Chlorella, were first manipulated in the following ways: (a) by changing the wavelength of the light source for photosynthesis; (b) by transferring the algae from autotrophic to dark heterotrophic conditions, (c) by growing the algae photoheterotrophically, and (d) by adding the inhibitory compound DCMU. Second, the hydrogen isotopic contents of different classes of compounds, carbohydrates, proteins, and lipids were determined. Third, the uptake of hydrogen from H20 into cellular organically bound hydrogen was studied by resuspending and growing algae in growth media H20 with a very slightly enriched deuterium content.