A deuterated biomolecule that significantly increases the effect of its protio counterpart
If thermodynamics is any guide, a biomolecule with hydrogen at a certain position might be expected to have deuterium there instead, about 0.015% of the time. (I.e., the natural occurrence of deuterium relative to protium is 150 ppm.) Here, kinetics is imagined to be the guide. Please picture the following: a bolus of a certain molecule appears, then is hydrogenated or deuterated with a certain isotope effect evident, then loses that H or D with another, different isotope effect showing. Because the first molecule is delivered in an isolated pulse (secreted, or released from one intracellular compartment into another), it can't be renewed or reach an equilibrium with its precursor. It decays, so to speak, along two paths, each leading to what appears to be the same molecule. Biologically, they ARE the same molecule. But because the deutero version itself decays at a slower rate, it may account for an outsize share of the total. If the molecule has some important but ephemeral biological activity, this "extra" share may be of some significance.
If this happens at all, I'd guess it's with a molecule with lots of tertiary carbons, like a prostaglandin or a steroid: something with a labile C-H (or C-D) bond. Let II be such a molecule. Its precursor I appears suddenly. Both [protio-II] and [deutero-II] will rise from zero to some peak, then drop. They will not necessarily peak at the same time, or stay proportionate throughout their short lives. What combination of rate constants and isotope effects will give us a good "deuterium bulge"?