On Thu, 17 Oct 1996 depreej at lincoln.ac.nz wrote:
> >:My interest is in deuterium oxide which contaminates all terrestrial
> >:water supplies at a ratio ranging from 1:5000 to 1:7000.
>> >Our water is contaminated with water? Oh, my!
>> >:It is a puzzle
> >:to me why so little research has been done on the deleterious effects of
> >:exposure to these concentrations over the human lifespan.
>> >There is no difference in chemical behaviour between the two, so why
> >would you expect any biological effects at all?
>> I used to think that too, but when I was a biochem student I remember covering
> this issue in one of our weekly lab meetings. Biochemists often study enzyme
> action using proton NMR (magnetic resonance). This may involve replacing
> many of the hydrogens in the substrate with deuteriums, or at least conducting
> the reaction in D2O. The professor assured me that this does cause a
> significant change in the rate of reation.
> D2O may be chemically the same as H2O, but in the confined space of an enzyme
> active site there is a difference.
>> Mind you, I doubt that the trace amounts of D2O in water will have any effect,
> I suspect that if the reaction doesn't favour D2O then H2O will crowd it out
> in nearly all cases.
>>> Jonathan Depree,
> Lincoln University, P.O. Box 84, Canterbury, New Zealand.
>> Socrates was a famous Greek Teacher who went around giving
> people advice. They killed him. (school history howler)
Just to add another intersting point, D2O also behaves slightly
differently than water in its osmotic properties, as is expected because
of its increased mass. I don't remember the references but I think it has
been demonstrated that cells (erythrocytes?) placed in D2O first contract
in volume and then swell and finally lyse [cells placed in water just
swell and lyse]. This has been observed in water with high amounts of D2O
too. This can be explained if one considers that D2O has a more difficult
time passing through pores(?) of the membrane as compared to water. This
can also be very easily simulated on the computer by assigning arbitrary
values to passage of water and D2O [assuming that these values for larger
solutes like Na+ is 0].
However the implications of this on living systems if contamination of
D2O increases is anybody's guess.
Aditya K Sengupta
Developmental Biology & Genetics Laboratory
Indian Institute of Science,
Bangalore 560 012, INDIA
email: aditya at serc.serc.iisc.ernet.in