We have previously shown that there are at least two ThDP pools, a larger low-turnover cofactor pool and a smaller high-turnover pool, precursor of ThTP and ThMP [49], [67].
Collagen turnover in animal and human tissues is rather complicated encompassing at least two pools of collagen, a soluble fast-turnover pool of procollagen/immature collagen monomers and a slower-turnover, insoluble pool of mature fibrillar collagen, which may be regulated independently [1].
In addition to this rapid-turnover ERC pool, we propose that multivesicular bodies represent the slow-turnover pool for HDL endocytosis (Fig. 1) [44].
For example 10% carbon from a high-turnover pool would only reduce a completely inert collagen C content of, e.g., 140 pMC to a reading of ∼137 (140 × 90% + 109 × 10%) due to dilution with carbon from the sampling year 2000 (109 pMC atmospheric value, Fig. 1).
Further studies suggest that HDL taken up by HepG2 and COS-7 cells is transported to two intracellular pools: A rapid-turnover retroendocytotic pool (half-life: 3.8 min) and a slow-turnover pool that is eventually further transported to lysosomes for degradation [48].
Key informants described that even despite this turnover, the pool of nurse graduates remains large.
The link between carbon turnover model pools and measurable carbon fractions is of key interest for initial parameterisation and subsequent validation of dynamic soil carbon models.
Therefore, as we do not know the size of the free high-turnover ThDP pool, this derivative was omitted from the equation.
That such cell populations are sustained at such a high level rather than recontracting is possibly explained by a relatively slow turnover of the pool, which may be maintained by regular antigen re-encounter and/or via cytokines.
