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/>2 H 2
et.), the presence of nonexchangeable deuterium atoms in amino acid side chains could only be synthesized de novo as the species with only covalent bonds -C 2
H, causes a decrease in protein stability.
These opposing effects do not cancel with the case of protein macromolecule, and fully deuteration of a protein often results in the destabilization. As for the deuteration of DNA macromolecule, today there are not reasonable considerations that such negative effect of 2 H 2
O on the structure and function is really existiting. Nevertheless, deuterium substitution can thus be expected to modify by changes in the structure and the conformation of both [U- 2
H]labeled DNA and protein, not only the reproductionl and division systems of a cell, and cytological or even mutagenical alterations of a cell, but to a greater or lesser degree of an order of a cell.
It should be noted, however, that not only these functions but also the lipid composition of cell membrane
are drastically changed during deuteration. The lipid composition of deuteriated tissue culture cells has been most complitely investigated by a certain scientists ( Rothblat et all., 1963, 1964).
As it is reported in these articles mammalian cells grown in 30% (v/v) 2 H 2
O contain more lipid than do control cells. THe increase in the lipids of 2 H 2
O grown cells is due primarily to increased amounts of triglycerids and sterol esters. Radioisotope experiments indicate that the differens are due to an enhanced synthesis of lipid. Monkey kidney cells grown in 25% (v/v) 2 H 2
O and or irradiated with X-rays likewise showed increases of lipid. The 2 H 2
O grown cells contained more squalene, sterol esters, sterols, and neutral fat

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