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By Michael J. Knight and others. Nature Communications 7, 11926 (16 June 2016). DOI: doi.org/10.1038/ncomms11926

Verified locators: Zinc silicate fluorescence, Figure 3; Proteoliposome transport assays, Figures 4–5; Discussion, near-neutral orthosilicic acid and sodium-dependent transport. The zinc signal is an indirect transport assay calibrated with silicic acid, not intrinsic fluorescence of free silicic acid.

Michael J. Knight is the first author of a 2016 study that reconstructed biological silicon transport using purified proteins. The investigators placed diatom silicon transporters in artificial liposomes, then measured entry of silicic acid with an internal zinc-dependent fluorescence assay. Applying a sodium gradient let them investigate transport outside the many interacting processes of a living biological cell.^[ref]

The measured transport saturated as the silicic acid concentration increased, with apparent Michaelis constants near 20 micromolar for two of the tested proteins. For an illustrative saturation law $v/V_{\max }=C/(K_M+C)$ with $K_M=20$ micromolar, increasing $C$ from 20 to 80 micromolar increases the predicted rate from $0.5V_{\max }$ to $0.8V_{\max }$, rather than multiplying it by four. The experiment therefore connects a mineral nutrient with a quantifiable molecular transport process. Its fluorescence signal came from an indicator reaction, so calibration and background controls were essential.^[ref]